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for the chemical and 
allied industries 

This BOOK gives a concise account of the 
sources, nature, modes uf occurrence 
and methods of treatment of all 
industrial minerals {except the hydro- 
carbons) and products derived from them, 
together with typical specification require- 
ments for their commercial use. There are 
also comprehensive bibliographies. 

The appreciative reception accorded by 
the technical press in many countries lo the 
first edition has encouraged the idea that a 
revised and enlarged edition might be 
equally welcome. A second edition has 
therefore been prepared bringing informa- 
tion and data as far as possible up to date. 

In preparing this second edition, con- 
sideration has been given to suggestions hy 
reviewers and readers of the book regarding 
desirable additional matter, and new 
chapters have been added on Diamond, 
Gold, Helium, Iron ores, Hafnium, Scan- 
dium and Yttrium, and the section on 
China Clay has been enlarged to cover other 
types of clays used for pottery, bricks, tiles, 
etc., and has been entitled "Clays". 

Since the date of publication of the first 
edition much information then on the 
''secret list" has been released ; advances 
in nuclear fission and electronics have been 
considerable, as lias progress in the produc- 
tion uf synthetic substances likely to prove 
competitive with products derived directly 
from mineral sources. Each section has 
therefore been carefully edited and, where 
necessary, chapters have been entirely 
rewritten in order to include as much new 
continued on Utn'k jltip 

Associated Bockj 
Pti blisters Ltd 

£8 ' 10 KET IK U.K. DULY 

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material as possible, particularly that 
relating to desirable qualities in metals 
intended for use in nuclear fission plant. 
Consideration has also been given to such 
synthetic materials as artificial sapphire and 
diamond, mica, and reconstituted quartz 
cry s Lais. 

This unique compendium should continue 
to prove of great value to the producers and 
consumers for whom it is primarily intended, 
but it will also be of assistance to technical 
information bureaux and professors and 
lecturers in universities and technical 
colleges having courses in industrial in- 
organic chemistry, economic geology and 


Catalogue No. 


Minerals for the Chemical 
and Allied Industries 


for the chemical and 
allied industries 



O.B.E., B.Sc.(Lond.), F.R.I.C., M.I.M.M. 

Technical Consultant 


Principal, Mineral Resources Department, 

Imperial Institute, London. 
Head, Commodities Intelligence Section, 
Ministry of Economic Warfare, London 




London: Chapman and Hall: 1961 

First published 1954 
Second edition 1961 



Catalogue No. 472/4 

Printed in Great Britain by The Whitefriars Press Ltd 
London and Tonbridge< 



The appreciative reception accorded by the technical press in many countries to the 
first edition of this book has encouraged the idea that a revised and enlarged edition 
might be equally welcome. A second edition has therefore been prepared bringing 
information and data as far as possible up to date in the limited space available. 

In preparing this second edition, consideration has been given to suggestions by 
reviewers and readers of the book regarding desirable additional matter, and new 
chapters have been added on Diamond, Gold, Helium, Iron ores, Hafnium, 
Scandium and Yttrium, and the section on China Clay has been enlarged to cover 
other types of clays used for pottery, bricks, tiles, etc. , and has been entitled " Clays." 

Since the date of publication of the first edition much information then on the 
" secret list " has been released; advances in nuclear fission and electronics have 
been considerable, as has progress in the production of synthetic substances likely 
to prove competitive with products derived directly from mineral sources. Each 
section has therefore been carefully edited and, where necessary, chapters have been 
entirely rewritten in order to include as much new material as possible, particularly 
that relating to desirable qualities in metals intended for use in nuclear fission plant. 
Consideration has also been given to such synthetic materials as artificial sapphire 
and diamond, mica, and reconstituted quartz crystals. 

At the suggestion of several correspondents details of the composition of a 
number of products marketed by specific firms have been included. Such details 
are intended solely to indicate the composition of materials available in the country 
of origin. The fact that data may refer to products marketed by one particular firm 
must not be taken as indicating that they are considered to be superior to, or more 
widely used than, those produced by other companies; they are intended merely to 
provide an indication of general requirements. 

It will be seen that details of the United States National Stockpile specifications 
have been retained in this edition, although stockpile purchasing in that country 
has practically come to an end. The reason for this retention is that some of the 
specifications are unique and, as a whole, they would seem to represent the optimum 
quality required by any purchaser of minerals or unprocessed metals. 

The authors would again like to express sincere thanks for valuable and willing 
help received from many parts of the world. A list of those who have been so kind 
is given in Appendix A. 

Special thanks must be expressed to Mr. E. H. Beard, B.Sc, Principal of the 
Mineral Resources Division of Overseas Geological Surveys, London, and to his 
staff; to Dr. John M. Warde and his colleagues in the New York office of the 
Union Carbide Ore Co. Ltd., and to Mr. Tom Hirst, A.R.S.M., D.I.C., M.I.M.M., 
of their London office, who have given much help and advice regarding many 
sections of this volume; to Miss R. Oblatt, Librarian of the Institution of Mining 
and Metallurgy, and to the Librarians and their staffs of the Chemical Society and 


of the British Standards Institution, for ready assistance and cooperation on many 

Acknowledgment is made to the Controller of H.M. Stationery Office, London, 
for permission to print certain tables from The Statistical Summary of the 
Mineral Industry; the British Standards Institution, for permission to reproduce 
extracts from over 100 of their standard specifications; the Commissioner of the 
Defence Materials Service of the United States General Services Administration, 
for permission to print extracts from the U.S. National Stockpile specifications; the 
American Society for Testing Materials, for permission to reprint extracts from over 
150 specifications. 

Sydney J. Johnstone 
17 Clifford Road, Margery G. Johnstone 

New Barnet, 
April 1961. 



During recent years substances of mineral origin have found increasing use in the 
chemical and allied industries, such as those producing ceramic materials, refrac- 
tories, building materials, paints, etc. The object of this book is to present in a 
concise form essential information on the properties of these minerals and metals, 
their sources of supply, processing and metallurgy, and uses with special reference 
to specifications laid down for their uses in particular industries. Those who have 
had occasion to seek such specifications know only too well the difficulties often 
attending the search, particularly where the requirements are not included in stan- 
dard specifications issued by well-known authorities. 

The material forming the basis of this volume first appeared in a series of articles 
by the writer in The Industrial Chemist and Chemical Manufacturer between August, 
1946, and April, 1949, and the author's thanks are due to the publishers of that 
journal for permission to utilize the substance of those articles in the present work. 
Since then, however, much new information has become available, particularly as 
a result of the lifting of the ban on the publication of information concerning 
developments in regard to sources of supply and utilization, which took place during 
World War II: such additional matter has been incorporated in the appropriate 
chapters. Indeed, in some cases subsequent developments have necessitated that 
whole chapters should be rewritten, as is the case with those on Aluminium, Arsenic, 
Bentonite, Bismuth, Cadmium and Cobalt. Furthermore, additional minerals and 
metals have been dealt with, notably Caesium and Rubidium, Calcium Chloride, 
Copper, Garnet, Germanium and Gallium, Greensand, Indium, Rhenium, Silver, 
Slate Waste, Tourmaline and Wollastonite. 

A selected bibliography of those publications which the author has found to be 
most useful has been added at the end of each section for readers who may require 
more detailed information on the individual materials. 

It has been found necessary to limit extracts from standard specifications to 
matters of chemical composition, but readers with specific interests are advised to 
consult the complete specifications, as these may, and often do, include require- 
ments in regard to physical properties. The appropriate addresses are: The Director, 
The British Standards Institution, 2 Park Street, London, W.l, and, The Director, 
American Society for Testing Materials, 1916 Race Street, Philadelphia, Pa., U.S.A. 
An endeavour has been made to include sufficient statistical matter to indicate 
not only the countries that are now the chief producers, but also those which were 
able, under wartime conditions, to ship increased quantities of certain materials. 

Readers who require more detailed statistics of the world's production, export 
and import of minerals and metals are advised to consult the annual volumes 
entitled Statistical Summary of the Mineral Industry: Production, Imports and 
Exports, which for many years previous to 1949 were prepared by the Statistical 
Section of the Imperial Institute, London, but are now prepared by its successor, the 
Statistical Section of the Mineral Resources Division of Colonial Geological 



Surveys, Imperial Institute, and published by Her Majesty's Stationery Office, 

Statistics showing the consumption of minerals and metals by particular industries, 
and especially the details of specific uses, are rarely obtainable in respect of the 
United Kingdom. For this reason, it has often been desirable to include official 
data published in the United States in order to indicate the trend of utilization and to 
afford actual and potential producers some useful idea concerning industries most 
likely to require considerable tonnages of a particular metal or mineral. 

Fluctuations in the market prices of industrial minerals are nowadays too 
frequent, and often too great to justify the inclusion of current prices in a book of 
this kind. Useful indications of the general trend of prices, particularly of the less 
common minerals, can be obtained from the comprehensive lists which are prepared 
in the Mineral Resources Division of Colonial Geological Surveys and published 
quarterly, by Her Majesty's Stationery Office in Colonial Geology and Mineral 

Although the original articles were primarily intended for producers and con- 
sumers of the products dealt with, the author has been pleased to find that they were 
of value to various technical information bureaux and also to teachers in technical 
colleges and other educational establishments. He hopes that the more up-to-date 
and extended information presented in this volume may prove valuable to an even 
wider circle of readers. 

The author would like to express his thanks to the many firms and individuals 
who have given him the benefit of their knowledge and experience, and especially to 
the many trade organizations, producers and users of mineral products in Great 
Britain and other countries of the British Commonwealth, the United States, France, 
Peru, etc., who kindly supplied information and, in some cases actually criticized 
and improved the manuscript. A list of those who have been so kind as to assist 
in this way is given in the Appendix. 

Special thanks are due to the author's colleagues in the Mineral Resources and 
Statistical Departments and Library of the Imperial Institute for their willing and 
valuable help in regard to material both for the original articles and for this revised 
and enlarged volume; to the Director of the British Standards Institution, to the 
Director, American Society for Testing Materials, for permission to reproduce 
numerous extracts from the Standards Specifications issued by their respective 
organizations, also to the Commissioner, U.S. General Services Administration, 
Emergency Procurement Services, Washington, D.C., for permission to print extracts 
from the U.S. National Stockpile Specifications issued by his Department. 

Last, but not least, the author acknowledges the valuable help which he has 
received from his wife in the critical revision of this volume for the press, in reading 
the proofs, and in preparing the Index. 

Sydney J. Johnstone 
17 Clifford Road, 
New Barnet, 
April, 1953. 




Prefaces v 

Introduction and General Bibliography 1 

Aluminium 5 

Antimony 30 

Arsenic 38 

Asbestos 41 

Asphalt and Bitumen 51 

Barium 59 

Bentonite 69 

Beryllium 75 

Bismuth 84 

Boron 89 

Bromine 99 

Cadmium 103 

Caesium and Rubidium 110 

Calcium Chloride (Natural) 114 

Chromium 116 

Clays 133 

Cobalt 145 

Copper 152 

Corundum and Emery 164 

Diamond 173 

Diatomaceous Earth 181 

Felspar 188 

Fluorspar and Cryolite 195 

Fullers* Earth 204 

Garnet 209 

Germanium and Gallium 211 

Gold 219 

Graphite 225 

Greensand 234 

Gypsum and Anhydrite 237 

Hafnium 249 

Helium 251 







Iron Ores 




Limestone, Chalk and Whiting 
















Niobium and Tantalum 




Ochre, Iron Oxide, Sienna, Umber 

and other Mineral Colours 






Platinum Group Metals 










Selenium and Tellurium 


Silica, Tripoli and Pumice 


Sillimanite Group 




Slate Waste 


Sodium Carbonate 


Sodium Sulphate 




Sulphur and Pyrites 


Talc, Soapstone, Steatite and Pyrophyllite 




Thorium and the Rare Earths 












Uranium and Radium 665 

Vanadium 686 

Vermiculite 696 

Wollastonite 701 




Appendix A — Acknowledgments 750 

Appendix B— International and Overseas Standards 

Organizations ' 55 






The author's experience, as Principal of the Mineral Resources Department of the 
Imperial Institute, London, was that there is a lack of correlated information avail- 
able to actual and potential mineral producers regarding the grades of product that 
will be acceptable for use in any particular branch of the chemical industry, and that 
there is need for closer liaison between the producers of crude minerals and those 
concerned with their industrial utilization. This condition, however, applies more 
particularly to producers of the non-metallic minerals, as the grades of the chief 
metallic ores suitable for smelting are fairly widely known. 

Chemical industry, however, consumes important quantities of metallic minerals, 
which are often required to be of higher grade than those intended for smelting, 
and to contain only small quantities of certain deleterious impurities. Although the 
production and marketing of such selected materials may be advantageous to the 
miner on account of the higher prices realized, he is often unaware of the specifica- 
tions to which his products must conform in order to be acceptable to the consumer. 

On the other hand, wartime experience brought to light new possibilities of 
substituting for one mineral product, which was then in short supply, another 
which had proved satisfactory, and it is hoped that some of the data given in this 
volume may prove useful in this connection to both users and producers. In 
general, it may be stated that few consumers in the chemical industry are willing to 
accept consignments of the crude mineral as mined, it being usually necessary to 
put it through some process, such as washing or hand picking; calcination; flotation, 
gravity, magnetic or electrostatic separation, before shipment. In many cases the 
consumer demands a product ground and sized to meet the requirements of his 
process, particularly with materials for use in the glass or paint industry or as fillers. 

Mineral producers should not assume that, because the product they are at 
present marketing is not regarded favourably by users in the chemical industry, an 
acceptable material could not be produced by suitable processing. This can only be 
decided by practical trials and careful consideration as to whether the cost of such 
additional processing is likely to be repaid by an enhanced price. 

Some producers of lesser known non-metallic minerals are unaware of the diver- 
sity of uses to which their products can be put, and it is hoped that they will be able 
to get some assistance on this point from the data given in this volume. 

Extracts from about 250 standard specifications, mainly British and American, 
are given in the relevant chapters, but space does not permit of any specifications 
being quoted in full. It is therefore suggested that readers should consult the com- 
plete specifications, which usually contain detailed instructions for carrying out the 
tests specified. Doubtless some readers will wish to obtain information concerning 
specifications in force in other countries, as well as those mentioned in this volume, 
and for their convenience a list of Overseas Standards Organizations (kindly sup- 
plied by the British Standards Institution) is given as Appendix B. This list could be 
considerably extended by the inclusion of certain Government Departments and 
many trade organizations which have formulated specifications independently for 


the products in which they are particularly interested. Mineral producers, however, 
should not assume that material which does not conform to a standard specification 
cannot be marketed. These specifications should be regarded more as representing 
the most suitable products which may be required for use in official or other 
important contracts for the purpose in question. 

Considerable diversity may occur in consumers' specifications for the same 
mineral, doubtless due to established customs, methods of processing at the users' 
works, availability of the raw material, price, etc. The data given may also serve to 
draw the attention of consumers to the possibility, in some cases, of employing less 
stringent specifications. 

It cannot be too strongly emphasized to the potential producer that the physical 
condition of the mineral may sometimes be a more important factor in determining 
its possibilities than is its chemical composition, good examples being micaceous 
haematite and many non-metallic minerals, such as graphite and mica for use in the 
paint industry, talc and abrasives. 

It also sometimes happens that a mineral product, which may be eminently 
suitable for one branch of chemical industry, is quite unacceptable for another, and 
it has not been possible to cover all such differences. The unsuitability may be due 
to the presence of small traces of impurities. 

Restrictions of the free market in minerals or metals, due to international 
conditions, government stockpiling, or other causes, usually result in numerous 
attempts to produce substitutes or to modify current practice so as to reduce the 
consumption of the material in short supply. Thus, during the Korean War restric- 
tive allocations of nickel in the United States resulted in the 18/8 stainless steel, so 
popular in the food processing and dairy industries, being replaced by a product 
containing less nickel. Chromium-manganese-nickel stainless steels containing 
1-5 per cent. Ni found favour and magnets, without nickel or cobalt, were made 
consisting essentially of manganese and bismuth. Substitutes for 18 per cent, 
nickel-silver were found in certain copper-based alloys containing only 4-5 per 
cent, nickel. The electroplating industry was also restricted in its consumption 
and in the thickness of deposits permitted. 

Restrictions on the export of minerals by some countries, occasioned sometimes 
by a desire to process the material in the country (often irrespective of the possi- 
bility of local markets being able to absorb the products), led consumers to seek 
other sources from which regular supplies could be obtained, irrespective of 
political controls. An example of this is the ilmenite and monazite occurring in 

Each of the following chapters deals with an individual mineral or metal and in 
no case has any attempt been made to give more than the salient points: indeed it 
would be impossible to do more in a book of this nature. More exhaustive details 
can be obtained from the sources indicated in the bibliographies given at the end of 
each section. 



The following list includes a number of publications which the authors have found of general 
use during the preparation of this volume and which may prove of assistance to those wishing to 
obtain more detailed information than it has been possible to give in this volume. 

Statistical Publications 

Statistical Summary of the Mineral Industry (world production imports and exports). Prepared 
by the Mineral Resources Division, Overseas Geological Surveys, London. (Annual. Recent 
issues cover six-year periods and include an extensive list of British Commonwealth and 
foreign statistical publications.) 

Annual Statement of the Trade of the United Kingdom with Commonwealth Countries and Foreign 
Countries. (Annual.) .-.„■> 

Bulletin of the British Bureau of Non-ferrous Metal Statistics, Birmingham. (Periodically.) 

Statistical Bulletin of the Aluminium Laboratories, Ltd., Banbury. (Periodically.) (Aluminium, 
magnesium, lead, zinc, tin, copper.) 

Minerals Yearbook; United States Bureau of Mines. (Annual.) 
Year Book of the American Bureau of Metal Statistics. (Annual.) 

Metallgesellschaft (Germany) Metal Statistics. (Annual.) 


" The Marketing of Metals." By J. E. Spurr and F. E. Wormser. New York, 1924, 674 pp. 

" A Comprehensive Treatise on Inorganic and Theoretical Chemistry." By J. W. Mellor. 16 vols, 

Lond., 1922-37 and supplements. 
" Standards and Specifications for Non-Metallic Minerals and their Products." By J. Q. Cannon, 

Jnr. US. Dept. Comm., Bur. Stand. Misc. Pub. No. 110, 1930, 690 pp. 
" Modern Uses of Non-ferrous Metals." Ed by C. H. Matthews. Amer. Inst. Min. Met. Eng., 

New York, 1935, 427 pp. 
" Strategic Mineral Supplies." By G. A. Roush. New York, 1939, 485 pp. 
" Catalytic Processes in Applied Chemistry." By T. P. Hilditch and C. C. Hall. 2nd Ed., Lond., 

1937, 478 pp. 
'* Catalysis." By S. Birkman, J. C. Morrell and E. Egloff. New York, 1940, 1,130 pp. 
" Refractory Materials: Their Manufacture and Uses." By A. B. Searle. 3rd Ed., Lond., 1940, 

895 pp. 
" Protective and Decorative Coatings." By J. J. Mattiello. 4 vols., 1942. (Vol. 2: Raw Materials, 

Pigments, Metallic Powders, Metallic Soaps. 658 pp.) 
" Reports on Refractory Materials." Iron & Steel Institute, Special Reports No. 26, 1939; No. 

28, 1942; No. 32, 1946. 
" Minerals in Industry." By W. R. Jones. Lond., 1943, 149 pp. 

" Reduction and Refining of Non-ferrous Metals." Amer. Inst. Min. Met. Eng., 1944, 555 pp. 
" Handbook of Non-ferrous Metallurgy." By D. M. Liddell. 2nd Ed., New York and London. 

1945. 721 pp. 
" Outlines of Paint Technology." By N. Heaton. 3rd Ed., Lond., 1947, 448 pp. 
" Encyclopedia of Chemical Technology." Ed. by R. E. Kirk and D. F. Othmer. New York. 1948. 

15 Vols, and supplement. 
" Inorganic Process Industries." By K. A. Kobe. New York, 1948, 371 pp. 
" Industrial Chemistry." By E. R. Riegel. 5th Ed., New York, 1949, 1,015 pp. 
" The Chemical Process Industries." By R. N. Shreve. New York, 1949, 975 pp. 
" Refractories." By F. H. Norton. 2nd Ed., 1949, 782 pp. 
" The Refining of Non-ferrous Metals." Inst. Min. Met., Lond., 1950, 534 pp. 
" Reports on the Progress of Applied Chemistry." Society of Chemical Industry, London. 

" Non-Metallic Minerals, Occurrence, Preparation and Utilization." By R. B. Ladoo and W. M. 

Myers. 2nd Ed., New York, 1950, 605 pp. 
" Rare Metals Handbook." By C. A. Hampel. New York, 1954, 657 pp. 
" Metals Reference Book." By C. J. Smithels. 2nd Ed., 1955. Interscience Pubs. 
" Dana's Manual of Mineralogy." By G. S. Hurlbut Jr., New York, 1959, 17th Ed., 609 pp. 
" The Chemistry and Physics of Clays." By A. B. Searle and R. W. Grimshaw. 3rd Ed., London, 

1959, 942 pp. 
" Industrial Minerals and Rocks (non-metallics other than fuel)." Amer. Inst. Min. Met. Petrol. 

Eng. 3rd Ed., New York, 1960, 984 pp. 
" Nouveau Traite de Chimie Minerale." Ed. by P. Pascal. 1956.— 20 Vols. 

b 2 


Although aluminium is the most abundant of the metallic elements in the earth's 
crust, the number of its ores used commercially as sources of the metal or its salts, 
is relatively few. The world's requirements are met principally by bauxite with 
smaller contributions from alunite, alum shale, leucite, and nepheline syenite. 
The aluminium bearing minerals bentonite, corundum, cryolite, felspar, fuller's 
earth, kaolin, kyanite and sillimanite are employed industrially, but not as sources 
of aluminium or its compounds, and are therefore dealt with elsewhere, as also are 
aluminous fireclays. According to a report on the Soviet aluminium industry by 
T. Shabard (1958) there is a strong trend towards the more extensive use, in the 
U.S.S.R., of non-bauxite minerals, such as nephelite, alunite, kyanite and 

At one time a pilot plant was operated by the U.S. Bureau of Mines at Laramie, 
Wyoming, to produce alumina from anorthosite, soda felspar carrying about 27 
per cent. AI2O3. It is claimed that the trials demonstrated the workability of the 
process in a commercial size plant. The output was sold mainly for refractory 

The name bauxite is applied to rock or earthy deposits in which the main 
constituent is aluminium which occurs principally as a hydrate, together with 
variable amounts of silica, iron oxide, titanium dioxide, and traces of some of the 
less common elements such as vanadium and beryllium. Silica is usually present as 
clay (hydrous aluminium silicate), but part may occur as quartz or sand. 

The aluminium may be present chiefly as the trihydrate, gibbsite, A1 2 3 .3H 2 
or as the monohydrate, diaspore or boehmite, A1 2 3 .H 2 0. In bauxites found in 
South America the aluminium is mostly present as the trihydrate and this is 
probably true of ore from deposits worked in Ghana, and Indonesia, and in some 
Indian deposits. In the French and most other bauxite deposits in Europe, the 
predominating mineral is the monohydrate. In some other deposits, such as those of 
Haiti and Jamaica, the aluminium may be present as both the mono- and trihydrate 
(principally the latter in Jamaica), mixed with other hydrates and hydrous oxides. 
As will be seen later, the degree of hydration of the alumina is of considerable 
importance as it determines the main details in the procedure used to extract the 
alumina from the ore. 

Sometimes it is possible to treat low grade bauxites so as to effect a separation of 
the gibbsite or the boehmite, which may be present as relatively hard particles, from 
the soft or finely divided clay minerals by a process of log washing. 

Clay minerals, iron oxide and titanium oxide are often so finely dispersed 
through the ore that physical methods of ore dressing, such as gravity, flotation, 
electrostatic or electro-magnetic separation, are not commercially successful. In 
general, it may be said that the separation methods used are more essentially 
chemical than physical and that bauxite is rarely beneficiated to any great extent by 
mechanical processes owing to the cost and difficulties involved. 

Bauxite mined in certain localities, notably in British and Dutch Guiana, before 


being shipped is crushed and washed to remove clay and certain other impurities. 
As the washed bauxite contains 15 per cent, or more of moisture, it is dried at 
about 93° C. to reduce transportation costs. With some bauxites, notably those from 
Ghana, it is possible to calcine at a higher temperature and so remove a consider- 
able proportion also of the combined water without affecting the solubility of the 
alumina in caustic soda solution. If the bauxite is intended for use in the manu- 
facture of refractory bricks or abrasives, it is sometimes further calcined at about 
982° C. to remove all the combined water which may amount to 25 or 30 per cent, 
of the ore. 

The chemical composition of cargo samples of typical bauxite from many 
countries is shown in Table 1. 

Table 1 

Analyses of Typical Bauxite Cargo Samples* 



Fe a O a 






Loss on 











British Guiana . 









Surinam . 































































Jamaica . 


















* From " The Chemical Background of the Aluminium Industry," by T. G. Pearson. 

Other elements sometimes found in bauxites, usually in amounts less than 0-1 
per cent., include beryllium, chromium, gallium, niobium, vanadium, zirconium 
and zinc. 

World Production 

The world's consumption of bauxite in the years immediately preceding World 
War II amounted to about four million long tons per annum, supplies coming 
chiefly from France, U.S.A., Hungary, British Guiana, Yugoslavia, Dutch Guiana, 
Netherlands East Indies, Italy and the U.S.S.R. 

World production of bauxite, which had been steadily rising for some years, 
in 1951 totalled about 11 million long tons and by 1956 had risen to about 17i 
million long tons per annum, of which about 6 million tons came from Common- 
wealth countries. Free world producers with outputs of over 1 million long tons 
(dry basis) in 1958 were, in order of importance, Jamaica, Surinam, United States, 
France and British Guiana. Perhaps the most outstanding occurrence in bauxite 
production has been the rapid increase in the output from Jamaica, which started in 
1952, with 340,000 long tons and had reached 5,722,000 long tons in 1958. An 


increasing amount of the bauxite mined in the island since 1952 has been treated 
locally for the production of alumina, of which 373,108 long tons was exported 
in 1958. 

Before 1939, British requirements were chiefly met by imported French bauxite 
which was classified for sale as follows: Red bauxite (low silica) containing AI2O3, 
56-60 per cent.; Si02, 3 per cent, (maximum); and Fe20 3 , 17 per cent, (maximum). 
White bauxite (chemical), AI2O3, 60 per cent, (minimum); Fe20 3 , 3 per cent. White 
bauxite (refractory), A1 2 3 , 50-60 per cent.; Fe 2 3 , l-\ per cent. Present require- 
ments are met by imports from Ghana, France, Greece and British Guiana. 

The world's production of primary aluminium now totals nearly 3-5 million 
long tons per annum. Of this amount the United States produces over 1 -4 million 
long tons, Canada about 566,162 long tons, whilst the U.S.S.R. and its satellite 
countries probably account for another 750,000 long tons. Other important smelters 
are France, Federal Germany, Norway, Italy and Japan. The United Kingdom has 
had a regular output of virgin aluminium around 30,000 long tons per annum for a 
considerable time, all produced by the British Aluminium Co. Ltd. United King- 
dom imports in 1958 included 186,311 long tons of aluminium ingots and 24,011 
long tons of alloys. Many countries augment their production of virgin aluminium 
by the recovery of secondary metal. Thus in 1957 the United States recovered 
323,053 long tons, Federal Germany 88,332 and Great Britain 108,835. 

United Kingdom exports in 1958 included 38,243 long tons of alumina, 34,841 
long tons of aluminium sulphate, 1 1,977 long tons of aluminium alloys in sheet and 
strip, etc., and 20,000 long tons of aluminium in the form of sheet, strip and plate. 

As a general rule, aluminium reduction plants are located close to large electric 
generating plants, owing to their heavy consumption of electric power. Electric 
generators powered by natural gas are now being used in the U.S.A., in addition 
to the more usual hydro-electric plants, and one is operated by lignite carbonized at 
low temperature. 

Uses of Bauxite 

The principal industrial uses of bauxite as a raw material are (1) for the produc- 
tion of metallic aluminium, (2) for the manufacture of salts of aluminium, (3) as a 

Table 2 

Consumption of Bauxites by Industries {U.S.A.)* 
Percentage of Total Consumption 







Alumina . . . 
Abrasives .... 
Chemicals .... 
Refractories .... 
Other uses .... 







Total consumption (dry basis) 
million short tons 







From " Minerals Yearbook," U.S. Bur. Mines (Annual). 


constituent of refractory bricks and other products, (4) for producing fused alumina 
(alundum) for use as an abrasive, (5) as a constituent of aluminous rapid hardening 
cement, and (6) in oil refining. A very large proportion of the world's output of the 
mineral is used for the first named purpose. 

The relative consumption of bauxite for industrial purposes in the United States 
is shown in Table 2. (see page 7) 

Of the U.S. domestic production in 1958, 14 per cent, contained less than 8 per 
cent, silica; 57 per cent, between 8 and 15 per cent.; and 29 per cent, more than 
15 per cent. 

Extraction of Alumina 

For the preparation of metallic aluminium or its salts, it is usually first necessary 
to extract the oxide (alumina) from the ore in a high degree of purity. It is true that 
during World War II a process for the direct reduction of metallic aluminium from 
low-grade ore was carried out to a limited extent in Germany, but the process is not 
generally applicable for the production of the commercially pure metal. In view of 
the world's decreasing reserves of high grade bauxite, it is evident that more attention 
will have to be given to lower grade mineral. 

Numerous attempts have been made to extract alumina from clay on a commer- 
cial scale. In 1956 the Anaconda Company announced that they had evolved a 
satisfactory process and had built a pilot plant at Anaconda, Montana, having a 
capacity of 50 tons per day, in order to test the process on a commercial scale. The 
United States Bureau of Mines has carried out extensive investigations on the pro- 
duction of aluminium-silicon alloys from clays in an electric arc furnace. So far as 
can be judged no process has been put into operation on a large scale for the 
extraction of alumina or aluminium alloys from clay. 

Many processes have been devised for extracting alumina from bauxite but the 
Bayer process is most generally used. 

Bayer Process. Bauxite is usually bought on its chemical analysis, a minimum 
percentage of alumina being required with maxima for silica and iron oxide. 
Standards in regard to composition often adopted in the U.S.A. range as follows: 
AI2O3, 55-62 per cent., with the following maxima for impurities: Si0 2 , 2-7 per 
cent.; Fe2C>3, 3-8 per cent.; and Ti0 2 , 2-4 per cent. The above percentages are 
calculated on the dried ore, which may still contain 25-32 per cent, combined water. 

As a general rule it is not economical to employ the Bayer process on bauxite 
which contains more than about 7 per cent, of silica, calculated on the dried ore. 
Each 1 lb. of silica present in the ore entails the consumption and loss of 1-2 lb. 
alumina and 2-3 lb. caustic soda. Usually ores carrying under 3 per cent, of silica are 
preferred. Oxides of iron and titanium should also be low as they function only as 
materials passing to the insoluble residue (" red mud ") which remains after the 
extraction of the alumina. Occasionally, however, bauxites containing as much as 
20 per cent, of iron oxide have been used for the production of metallic aluminium. 
The " Alcoa Combination Process," a cyclic method for treating high silica bauxites 
devised in the Aluminum Research Laboratories of the Aluminum Co. of America, 
embodies the features of both the Bayer and lime-sintering processes. The " red 



mud " residue from the Bayer treatment, mixed with limestone and soda ash, is 
sintered at 1,800-2,000° F. and the sinter is leached with caustic soda solution, which 
dissolves most of the alumina and only small amounts of the silica. This caustic 
leach is then added as a part of the charge in the regular Bayer digest. The process, 
now in use at two works in Arkansas, is claimed to extract economically from 85 to 
90 per cent, of the alumina present in high silica bauxites, as compared with 70 per 
cent, or less recovered by the normal Bayer process from similar material. 

The product marketed is almost entirely calcined alumina which is used chiefly 
for the extraction of the metal and also in the abrasive, refractory and ceramic 
industries, but hydrated alumina, tabular alumina and other special products are 
also made. 

The U.S. National Stockpile Specification P-5a-R, dated August 19th, 1952, for 
the purchase of bauxite suitable for the production of metallic aluminium by the 
Bayer process, provides for two types of ore which should have the following 
percentage compositions, calculated on a dry basis. 


Mixed Monohydrate 


— Trihydrate Ore 

Per cent. 

Per cent. 

Alumina, A1 2 3 , min 



Silica, Si0 2 , max 



Total Alkalis (as oxides), max. 



Ferrous iron, FeO, max 



Phosphorus, P 2 5 , max. . . . . 



Manganese, Chromium and Vanadium 

calculated as Mn0 2 , Cr 2 3 , V 2 6 , max. 



Loss on ignition, max. .... 

50 per cent, of 

40 per cent, of 

actual Al 2 O a 

actual Al 2 O s 

* A1 2 3 = 100 less total percentages of silica, iron oxide, titanium dioxide and 
loss on ignition. 

t Al 2 O a = difference between percentage of R 2 O a oxides and the sum of per- 
centages of Fe 2 3 , TiO a and P 2 6 . 

Of the substances other than aluminium hydrate present in the crude bauxite, 
titanium (which usually occurs as rutile) zircon and niobium minerals remain in the 
red mud from the Bayer process as also do minerals containing chromium, but 
traces of the latter may pass to the alumina. Gallium passes into solution in the 
Bayer process and tends to remain in the liquid after the precipitation of the 
aluminium hydrate. Vanadium is partly soluble during digestion in the process and 
is an objectionable impurity as it tends to make the alumina unsuitable for the 
production of aluminium sulphate and increases the electrical resistivity of metallic 

The details of the Bayer process differ according to whether the alumina is 
present in the ore as the trihydrate or as the monohydrate. The essential difference 
between the behaviour of the two hydrates is that the trihydrate is the more readily 
soluble in caustic soda and can be extracted by digestion with alkali at temperatures 
only slightly above boiling point at atmospheric pressure. Monohydrate ores, on the 


other hand, require treatment with more concentrated alkali under pressures up to 
1801b. per sq. in. 

In the Bayer process, as used in Great Britain, the ore is crushed to 10-mesh and 
digested with caustic soda solution for about eight hours at 180 lb. per sq. in. 
pressure. The charge is then blown, under its own pressure, into a flash chamber and 
mixed with wash-water from a later stage of the process. The larger undissolved 
particles are then separated from the liquid which is diluted and any silica which has 
passed into solution is precipitated as sodium aluminium silicate. After this opera- 
tion, the remaining insoluble matter is removed by filtration and the clear liquor is 
then pumped to the decomposing vessels where the aluminium is precipitated, in a 
crystalline form, as hydrate. This precipitation is accomplished by cooling the 
solution, adding some precipitated aluminium hydroxide, known as " seed," and 
stirring by paddles or submerged airlift for three to five days. The quantity of 
" seed " added may vary between 25 and 100 per cent, of the alumina in solution. 
The particle size of the precipitate varies with the degree to which the solution has 
been cooled and its concentration. This process usually precipitates from 50 to 
60 per cent, of the alumina in solution. 

The precipitate is next washed to remove alkali and if required for the production 
of metallic aluminium, calcined in oil or gas-fired rotary kilns at about 1,400°C. 

The composition to which makers in Europe and the United States endeavour to 
work for the alumina varies somewhat as shown in Table 3. 

Table 3 

Alumina Specifications 

United States 


Per cent. 

Per cent. 

Silica, SiO a 


< 010 

Ferric oxide, Fe a 3 

< 003 


Titanium dioxide, Ti0 2 

< 0002 


Soda, Na s O .... 



Loss on ignition 

< 0-50 



+ 100-mesh .... 



+ 200-mesh .... 



+ 325-mesh .... 



— 325-mesh .... 


63 or more 

A good account of the theoretical and practical considerations underlying the 
Bayer process and its practical application is given by T. G. Pearson in " The 
Chemical Background of the Aluminium Industry," who also describes some of the 
numerous processes which have been devised to replace the Bayer method. He 
concludes that as yet there is no method which can compete with this process for 
making alumina for aluminium production. Certain other processes, however, 
operating under specially favourable conditions have been in use for some years, 
notably the Pedersen process operated at Hoyanger in Norway, where a mixture of 
bauxite, limestone, gas coke and iron ore are smelted in an electric furnace. Other 



lengthy accounts of methods are given in Gmelin's Handbuch der anorganischen 
Chemie and by Frary and Jeffries in their bulletin The Aluminium Industry. 

Reduction to the Metal 

The metal is produced by the electrolysis of a molten mixture containing 
anhydrous alumina dissolved in cryolite (sodium aluminium fluoride) to which 
have been added small quantities of fluorspar and aluminium fluoride. The fused 
mixture is contained in a steel box which is lined with carbon 6 to 10 in. in thickness. 
The anodes are prepared from high grade coke, usually petroleum or pitch coke, 
having a very low ash. Each cell takes from 8,000 to 100,000 amperes (according to 
size), at a voltage of 4 i to 6£ per cell. The current consumption averages about 
10 kw. hrs. per lb. of aluminium metal produced. 

Some of the physical properties of pure metallic aluminium are as follows : 

Atomic number 13 

Atomic weight 26-97. 

Crystal structure Face-centred cubic. 

Melting point 660 -2°C. 

Density (at 20°C.) 2-699 g./cm. 3 

097 lb./in. 3 
Thermal conductivity 

(at 20°C.) 0-503 cal./sec./cm./°C. 
Thermal neutron absorption 


Microscopic 0-215 barn*/atom. 

Macroscopic 0-014 cm. -1 

Specific heat (at 20°C.) 0-208 cal./g./°C. 
Coefficient of linear expan- 

sion(20-100°C.) 23-8 x 10-«per°C. 

Young's modulus (at 20°C.) 9-7 x 10 6 lb./in. 2 

* 1 barn = 10" 24 cm. 2 

The ever increasing use of aluminium and its alloys for diverse purposes in 
industry has led to the formulation of numerous specifications by the British 
Standards Institution, the Directorate of Technical Development of the Ministry of 
Supply, the American Society for Testing Materials and other official bodies. 
Independently of these, a number of other organizations have formulated their own 
specifications, such as Lloyds, Bureau Veritas and Registro Italiano, all of which are 
concerned with shipping. The British Standard Specifications may be roughly 
grouped into : (1) aluminium and its alloys for general engineering purposes covered 
by B.S. 1470-77 for wrought forms, and B.S. 1490 for ingots and castings, (2) 
aluminium for electrical purposes, dealt with in the B.S. 2627 series and (3) aircraft 
materials, covered by the L series of British Standard Specifications. There is also 
the D.T.D. series issued by the Directorate of Technical Development, Ministry of 





■* -a 
1 § 







o g 
a p 




-p e 




























So 2 
b S3 'a 



In Table 4 are shown the chemical compositions of a few of the types of alumin- 
ium ingots included in the series of British Standard Specifications for general 
engineering purposes (LM series), aircraft construction (L series) and the Director- 
ate of Technical Development of the Ministry of Supply (DTD series). 

A useful summary of the chemical composition and physical properties required 
by most of the British Standard Specifications is given on pp. 22-133 of " The 
Properties of Aluminium and its Alloys " issued by the Aluminium Development 
Association and the same document also gives a lengthy list of British proprietary 
brands of aluminium and its alloys related to B.S. 1470-77 and 1490. 

The U.S. National Stockpile Specification P-62-R1 dated July 30th, 1954, 
requires pig aluminium metal to have the chemical composition shown in Table 5. 

Table 5 

Aluminium (Pig). U.S. National Stockpile Specification P-62-R1. 30th July, 1954 
Chemical Composition 

Per cent, by weight 

A to b 

Min. Aluminium 


99-90 to 99-65 

by weight 


Min. Aluminium 


99-60 to 99-20 

by weight 

Silicon + Iron (max.) 

Copper (max.) 

Manganese (max.) 

Chromium (max.) 

Zinc (max.) 

Nickel (max.) 

Other elements each (max.) .... 
Total elements other than Aluminium, Silicon, 

Iron (max.) 

Difference — Aluminium (min.) 





Refining of Aluminium. The purity of the metal obtained by normal reduction 
methods is usually between 99-5 and 99-8 per cent, aluminium, but metal containing 
99-8-99-9 per cent, aluminium can be obtained by the use of specially selected raw 

Aluminium cannot be refined by the methods normally used for many other 
metals, as it is more electro-positive than most metals except those of the alkali and 
alkaline earth groups. Also it cannot be purified by straight distillation processes 
owing to its high boiling point (about 2,500 C C.) and the difficulty of finding suit- 
able furnace materials. 

According to T. G. Pearson, who gives a good survey of methods which have 
been proposed for refining aluminium on a commercial scale, the operation has 
only been carried out with the aid of molten salt electrolysis. Super-purity alu- 
minium is very ductile and readily worked and has therefore been used for roof 
flashings and coverings where severe deformation is involved. Such material is 



covered by British Standard Specifications B.S. 1470 and 1475. The strength of 
super-purity aluminium can be considerably increased by alloying it with small 
quantities of manganese or magnesium or magnesium and silicon followed by heat 

The world's annual production of super-purity aluminium now probably totals 
about 10,000 tons. 

Uses of Metallic Aluminium 

The outstanding physical characteristics which give aluminium its value in 
industry are its lightness, high strength in proportion to its weight, and resistance to 
atmospheric and many types of chemical corrosion. Its relatively high electrical 
conductivity also enables it to compete with copper in this respect for many purposes. 
Aluminium and many of its alloys can be rolled, pressed, extruded, spun, drawn 
and stamped to the desired form. 

An important use for aluminium is as the major constituent of alloys with other 
metals, such as magnesium, copper, nickel, cobalt, tin and zinc. It is used in die- 
casting alloys containing silicon, silicon and copper, or silicon, copper and nickel. 
Its wrought alloys include such metals as manganese and copper-nickel. Sand- 
casting alloys containing aluminium are very numerous and often include 
magnesium, copper, nickel and silicon. 

For several years past, the largest consumer of aluminium in the United States 
has been the building trade, in which the metal is used principally for roofing, 
siding, window frames, shingles and ducts for heating and ventilating. It is also 
being increasingly used in aircraft construction, structural engineering, shipbuilding 
and the manufacture of railroad rolling stock. Aluminium reinforced with steel is 
also extensively used as a conductor for electric power. 

The Aluminum Association (United States) estimated that for the period 
January to June 1958 wrought aluminium products represented about 80 per cent. 
of all shipments of aluminium in the United States; followed by die-castings, 
permanent mold castings and sand-castings. Of the wrought products sold 22-5 per 
cent, was used for building materials, 13-3 per cent, by the transport industry and 
10-3 per cent, by the electrical industry. Nearly 58 per cent, of the permanent mold 
castings produced was used in transportation motor vehicles (except military). 
About 43 per cent, of the aluminium sand-castings went to makers of industrial 
and commercial machines, equipment and tools. 

Electrical Industry. The most important use for aluminium in this industry is for 
the transmission of electricity from the generating station to distributing sub- 
stations. Although aluminium has greater bulk than copper for the same resistance, 
its density is much lower and for equal resistance an aluminium conductor is 
approximately \\ times the cross-sectional area of a copper one, but only half the 
weight. The mechanical and electrical properties of electrical purity aluminium are 
given in British Standard Specification B.S. 2627 : 1955. Steel cored aluminium 
conductors have been in use for over 50 years for overhead transmission. More 
recently steel cored aluminium alloy conductors have found use for special purposes, 
the alloy being one of aluminium, magnesium and silicon. Steel cored aluminium 



cable has been used for telecommunications since 1926 and more recently high 
frequency co-axial cables consisting of a copper conductor and aluminium sheath 
have been brought into use. 

Aluminium wire has also been used abroad in the field windings of alternating 
current generators. 

Building Construction. As indicated above, for some years past the largest 
consumer of metallic aluminium in the United States has been the building trade, 
and in Great Britain this use has increased very considerably in post-war years, 
particularly for roofing, siding, window frames, shingles and ducts for heating and 

The use of aluminium for cladding buildings has been described in detail by 
E. H. Laithwaite and E. W. Skerrey of the British Aluminium Company. It is 
stated that after a series of practical trials the Gas Board are using aluminium for 
roof and side wall coverings at gasworks, and the Central Electricity Board is 
employing the metal for roofs and walls of power stations. Aluminium roofing is 
also finding wide application in industry and agriculture. 

A number of specifications for aluminium products for use in building have been 
formulated by the British Standards Institution, sheet material being covered by 
B.S. 1476 : 1955 for wrought aluminium and aluminium alloy sheet and strip; 
aluminium fixing accessories for building purposes by B.S. 2465 : 1954; aluminium 
rainwater goods, cast and extruded, by B.S. 1430 : 1947; wrought aluminium 
rainwater goods by B.S. 1543 : 1949. 

The composition and mechanical properties of aluminium alloys for some 
engineering uses in the form of sand, gravity or pressure diecastings is included in 
British Standard Specification B.S. 1490 : 1955, which enumerates six classes of 

Nuclear Fission. Aluminium and some of its alloys have found considerable use 
in nuclear energy projects, as the metal, in common with certain other light metals 
such as beryllium or magnesium, is not affected to any great extent by nuclear 
bombardment. Neutrons tend to pass through aluminium without their speed or 
intensity being much altered and the chances of direct hits by neutrons are therefore 
relatively few. When a neutron is captured and the metal becomes radioactive the 
activity is short-lived. 

One important use for aluminium has been as a sheath (can) to protect uranium 
fuel rods in the atomic pile from attack by the atmosphere of the cooling medium. 
Aluminium reacts with uranium at about 175°C, and so the temperature at which 
aluminium can be used as a canning material is limited. Certain aluminium alloys 
containing nickel and iron have been developed, however, which can be used up to 

The metal has good thermal conductivity and so facilitates the transfer of heat 
from the uranium fuel rods to the coolant. It is not affected by air or carbon dioxide 
up to near its melting point and can withstand pure water or heavy water up to 
about 150°C. 

In addition to its use as a canning material, aluminium (99 to 99-5 per cent, 
metal) is extensively used in plants at nuclear reactors and alloys of aluminium- 



magnesium and aluminium-manganese have been used in plant at Harwell, Alder- 
maston and Dounreay. 

The standard adopted by Atomic Energy for Canada Ltd. for reactor grade 
aluminium specifies the following maximum percentage limits for impurities : 

Copper, Cu 


Chromium, Cr 





Gallium, Ga 





Vanadium, V 


Nickel, Ni 


Cadmium, Cd 


Titanium, Ti 


Cobalt, Co 


Zinc, Zn 


Iron, Fe 


Boron, B 


Silicon, Si 


A material known as "Boral," first developed by the U.S. Atomic Energy 
Authority at their Oak Ridge plant, consists of a core of boron carbide dispersed in 
aluminium powder and clad on both sides with aluminium sheet. This material is 
claimed to give neutron shielding, equal to 26 in. of concrete, from neutrons of 
relatively low energies. It has been used in partial substitution for concrete in some 
experimental reactors which develop high neutron flux densities. It is made on a 
commercial scale by the Aluminum Company of America. 

Aluminium has been used in some component parts of guided missiles, notably 
in the centre and top sections, the tail and the spin launcher. 

Equipment for handling Food Products. As aluminium is hygienic, non-toxic and 
free from attack by many chemicals, it finds wide use for domestic cooking utensils, 
and in industry for tanks, containers and processing vessels, such as brewing vats, 
steam-jacketed boiling pans for the preparation of meat and fish products, refrigera- 
tors and cold-storage rooms. In Norway aluminium is used extensively for containers 
for canned fish. The use of a decorative protective coating of porcelain enamel 
fired on to aluminium for many domestic articles, such as washing machines, 
is increasing. The product which can be made by ordinary vitreous enamelling 
procedure can be sawed or drilled without damage to the coating. 

Packaging. Aluminium foil is being extensively used as a wrapping material 
to replace tinfoil, as a heat insulating material and in electric capacitors. Aluminium 
foil is usually rolled from metal of at least 99 per cent, purity into sheets not more 
than 006 in. thick, but for electrical capacitors a thickness of only 0002 in. is 
required. For packaging it is frequently laminated to other materials such as paper, 
plastics, cloth, etc., or it may be protected by lacquers. Such packaging materials 
are dealt with in British Standard Specifications B.S. 2758 : 1956 for " vegetable 
parchment/aluminium foil laminates (parchfoil) for wrapping dairy and other 
products " and B.S. 1683 : 1950 is for coated aluminium foil for wrapping cheese. 

The requirements for certain anodized films are dealt with in British Standard 
Specification B.S. 1615:1958 on anodized aluminium. The Aluminium Develop- 
ment Association of London has issued an informative bulletin entitled The 
Anodic Oxidation of Aluminium and its Alloys. 

Brazing. Aluminium-silicon as a brazing filler metal is dealt with in A.S.T.M. 
Tentative Specification No. B 260-52 T, which covers four grades. The Specification 



was prepared jointly by the American Welding Society and the A.S.T.M. and requires 
the metal to have the chemical composition shown in Table 6. 

Table 6 

Aluminium-Silicon Brazing Filler Metal, A.S.T.M. Standard B 260-52 T 




Per cent. 

Per cent. 



Per cent. 









BAlSi.K 1 ) 
BA1SL3( 2 ) 



















1 Including titanium 0-20 per cent. 

2 Including chromium 01 5 per cent. 

In each of the above classifications the limit for other elements, each, is 005 per cent, 
and totals 015 per cent. In all cases aluminium makes up the remainder of the alloy. 
Single values shown in the above table are maximum percentages, except where otherwise 

The brazing filler metals Nos. 1, 2 and 3 are stated to be most suitable for brazing 
certain grades of aluminium and aluminium alloys with the furnace and dip processes. 
No. 4 is most suitable for the torch brazing process, but can be used with the furnace 
or dip process. 

Alum inium alloys in powder form are used in the manufacture of welding elec- 
trodes. Some of those made by Murex Ltd. of Rainham, England, include alloys of 
aluminium with chromium, copper, iron, manganese, magnesium, nickel, silicon 
and titanium. 

Metallurgy. Aluminium for use in the manufacture of iron and steel is covered 
by A.S.T.M. Standard No. B 37-57, which requires the metal to comply with the 
requirements as to chemical composition shown in Table 7. 

Table 7 

Aluminium for Iron and Steel Manufacture, A.S.T.M. Standard B 37-57 




Per cent. 

min. by 
Per cent. 


Per cent. 



Per cent. 



Per cent. 

Total of all 

Per cent. 


95 to 97-5 
92 to 95 
90 to 92 
85 to 90 














Aluminium finds use as a deoxidizing agent in the casting of steel. 

Aluminium powder, owing to its great affinity for oxygen, is a powerful reducing 
agent for many metallic oxides and finds application in the production of numerous 
metals by the so-called " Thermit " process. It is also used in welding iron and 

Aluminium powder is used for metallizing processes in which powder is used 
instead of a stream of molten metal, and for deoxidizing purposes in some foundries 
dealing with ferrous alloys. The wide range of atomized aluminium powder made 
by Murex Ltd. of Rainham, England, includes grades ranging in purity from 90 to 
99 per cent, and in size from a coarse material (8-mesh/down) to the finest grade 

A number of aluminium alloys are used as hardeners for other metals, and those 
produced in powder form and marketed by Murex Ltd. include manganese- 
aluminium (usually 10 per cent. Mn); titanium-aluminium (2, 5, 10, 20, 50 and 
65 per cent. Ti); titanium-copper-aluminium (20-25 per cent. Ti, 50-55 per cent. 
Cu, and the balance Al). Nickel-aluminium containing either 42 or 52 per cent. Ni 
is finding increasing use in the preparation of nickel catalysts. 

Pigments. Metallic aluminium finds considerable use as a protective pigment in 
anti-corrosion paints. For this purpose it is specially prepared in the form of flakes, 
which are produced by stamping small pieces of the pure metal, together with a 
lubricant, in stamp mills or ball mills, screening to size and then polishing. The 
latter operation is usually conducted in a special steel drum, using stearic acid as a 
lubricant. After polishing, the flakes are packed into drums and stored for a few 
weeks to age or " fix " the film of polishing agent on the flakes so that they will 
" leaf " properly when incorporated in paint. 

The most valuable feature of aluminium flake pigment is its property of " leaf- 
ing," when suspended in a suitable vehicle, to form an almost continuous metallic 
layer at the surface of the paint and so protect from moisture. 

Aluminium metal pigments are usually graded according to the size of the 
flakes; commonly two grades are marketed — (a) regular powders or varnish grade, 
and (b) " fine " or " lining " powders. 

British Standards Institution Specification B.S. 388 : 1952 for aluminium 
(powder and paste) for paints, requires the powder to be in the form of flakes. 
Copper must not exceed 05 per cent, and matter volatile at 98 to 102°C. is 
limited to 0-5 per cent. Tests are also specified for leafing properties, water covering 
capacity, colour and opacity to correspond with those of a sample agreed between 
buyer and seller. 

Standard specifications for aluminium pigments, powder and paste for paints are 
included in A.S.T.M. D 962-49, in which aluminium pigment powders for use in 
paints are divided into three classes : (a) standard lining fineness for general paint 
uses; (b) extra fine lining fineness for special finishes; (c) standard fineness for special 
uses where a coarse finish is desired. The aluminium pigment powder must consist 
of commercially pure aluminium in the form of fine polished flakes, and a suitable 
fatty lubricant. It shall contain no filler or adulterant, such as mica. The specification 
requirements in regard to composition are shown in Table 8. 



Table 8 

Aluminium Powder for Paints. A.S.T.M. D 962-49 

Non-volatile matter at 105-110° C, min 

Easily extracted oily and fatty matter (polishing lubricant), max. 
Total impurities, other than oily and fatty matter, max. . 
Course t)£Lrticlcs * 

Class (A), total residue on No. 325 (44 micron) sieve, max. . 

Class (B), „ „ „ „ „ ,. „ max. . 

Class (C), „ „ „ No. 100 (149 micron) „ max. . 
Leafing, min. 

Class (A) 

Class (B) 

Class (C) 

Per cent. 



The above specification is identical with U.S. Federal Specification TT-A-468a 
of October 7th, 1949. 

Anodized Aluminium. Aluminium and its alloys are frequently given a protective 
coating by the electrolytic process known as anodizing. This process is the reverse 
of electroplating, as the film is formed on the anode and the base metal is progres- 
sively oxidized beneath the anodic film, so that the last portion to be formed is that 
next to the metal. Chromic anodizing is commonly used in the case of aluminium 
and its alloys and is carried out with a 5-10 per cent, solution of chromic acid, at a 
temperature of about 95° F., by low voltage direct current for about thirty minutes. 
Aluminium alloys containing up to 5 per cent, of copper can be anodized in this way 
and metal so treated can be dyed in a variety of colours. 

Chemical Industry. Aluminium powder finds use as a reducing agent in a wide 
variety of chemical processes. It is also employed, to a limited extent in making 
aerated concrete, in explosives and pyrotechnics. 

Al uminium Salts 

The ore employed for the production of pure alumina and salts, such as the 
sulphate, chloride, hydrate, acetate, sodium aluminate and the alums, should have 
an AI2O3 content as high as possible, preferably over 52 per cent. Ores carrying 
Si02 up to 1 1 per cent. ; Fe203, l-2£ per cent. ; and Ti02, 1-3 per cent, may be used. 
A low iron content is most desirable and the alumina in the ore should be readily 
soluble in sulphuric acid. Some British makers of aluminium compounds do not use 
bauxite as their raw material, but employ pure aluminium hydrate or alumina which 
they purchase from firms operating the Bayer process. 

The quantities of some aluminium salts produced in the United States in 1957 
are shown in Table 8a 

Aluminium Sulphate. This is the most important of all aluminium salts. The two 
main grades marketed commercially are often termed " iron-free," which actually 
contains about 0003 per cent. Fe203, and " commercial " or ferrous, which has a 
total iron content equivalent to about 0-4-0 -5 per cent. Fe203. 



Table 8A 
Production of Selected Aluminium Salts in the U.S.A. in 1957* 

(short tons) 

No. of plants 

Aluminium sulphate: 


Commercial (17 per cent. A1 2 3 ) .... 



Municipal (17 per cent. A1 2 3 ) ..... 



Iron Free (17 per cent. A1 2 3 ) 



Sodium aluminate (62-2 per cent. A1 2 3 ) .... 



Aluminium chloride: 

Liquid and crystal (32° B) 



Anhydrous (100 per cent. A1C1 3 ) 



Aluminium fluoride (technical) 



Aluminium trihydrate (100 per cent. A1 2 3 .3H 2 0) 



*From " Minerals Yearbook," U.S. Bur. Mines. 

Chemical analyses of several commercial grades of aluminium sulphate marketed 
in Great Britain are shown in Table 9. 

Table 9 

Chemical Composition of Commercial Aluminium Sulphate (}). 





with free acid 

15-18% O 

Iron Free 


Iron Free 



Insoluble . 







Alumina, AI2O3 . 







Ferrous Oxide, 




Ferric Oxide, 

V 0-003 


y o-oo3 



V 0-003 

Fe 2 3 . 







FreeSOs . 







Combined SO3 . 







Water (by differ- 








(*) From "Aluminium Sulphate " — The Alumina Co. Ltd., Widnes, Lanes. 
( 2 ) Also contains lead 50 p.p.m.; arsenic 10 p.p.m. 

Aluminium sulphate is supplied in various forms according to user's require- 
ments, including (1) slabs weighing up to 56 lb. for use where a continuous dissolv- 
ing process is used, (2) material crushed to pass 3 in. or 4 in. mesh, (3) kibbled and 
screened and (4) ground and kibbled. 

Large quantities are used in the paper industry for fixing the size which is added 
to the paper pulp just before it goes to the paper-making machine. Aluminium 
sulphate for this purpose is usually low in iron and contains from 17 to 18 per cent, 
of AI2O3. Aluminium sulphate containing from 14 to 15 per cent, of AI2O3 is used in 



large amounts as a coagulant and precipitating agent in the treatment of sewage and 
drinking water. 

Aluminium sulphate is also used in certain processes for rainproofing textiles, 
and in the preparation of colloidal aluminium hydroxide for pharmaceutical 

A certain amount of aluminium sulphate for use in sewage treatment is made by 
heating the residue, " red mud," from the Bayer process of extracting alumina from 
bauxite, with sulphuric acid. The product, which contains more sulphate of iron 
than sulphate of aluminium is often supplied in liquid form. 

A product known as " alum cake " is made by treating calcined china clay with 
96°Tw. sulphuric acid, and breaking up the pasty mass so obtained. The product 
carries 12-13 per cent, of soluble AI2O3, 01-O-2 per cent. Fe 2 3 , 0-4-1 per cent, 
free H2SO4 and 20-24 per cent, insoluble matter. 

Alums. Formerly, most of the requirements of Great Britain for alum were met 
by products made by burning alum shale in heaps, exposing to the air to oxidize 
ferrous sulphide to sulphate and oxide, and lixiviating with water. After adding the 
requisite amount of potassium chloride, the salt was allowed to crystallize out. 

In more modern processes alum is made from clay or other aluminium silicate or 
bauxite, but sometimes alunite is used. In the usual process the mineral is roasted, 
ground and sieved and the fine powder is treated with sulphuric acid (about 1 -53 
sp. gr.) at 70-100°C. The aluminium sulphate formed is dissolved in hot water, 
separated from the insoluble matter, and the solution is added to a hot saturated 
solution of potassium sulphate. On cooling, impure potash alum is deposited in the 
form of small crystals (alum meal) which, after being washed, are purified by 

Alum is used for making lake pigments and some mordants, such as the acetate 
and sulpho-acetate. For use with certain of the more delicate shades of dyes the 
alum must be practically free from iron compounds: in some cases even 01 per 
cent, may be too high. Alum is also used in dressing skins (" tawing ") to produce 
white leather; in sizing paper and for waterproofing fabrics. For a number of uses 
aluminium sulphate can replace alum. 

Aluminium Chloride. This salt is marketed in three forms, i.e. liquid, crystal and 
anhydrous. The principal uses for the anhydrous salt are as a catalyst in organic 
chemistry operations involving condensation, dehydration, reduction, polymeriza- 
tion and cracking. The crystal and liquid forms are used chiefly in the soap industry 
for salting out glycerine lyes and to a less extent as a wood preservative and as a 
disinfectant in water treatment. 

Aluminium Stearates. A number of these products are marketed under several 
trade names and contain varying proportions of stearic acid. They are all white 
powders and are used as waterproofing agents for ropes, insulated wrappings and 
carriers; as antioxidants in transformer oils; as suspending agents in insecticides 
and disinfectants; in floor polishes and dry-cleaning compounds; in artificial 
thickening compounds in mineral and vegetable oils; and in the manufacture of 
paint and varnish, both as flatting agents and to reduce the rate of settling of 



The composition of three typical products are as follows: 


Softening Point 

Aluminium mono-stearate 

Aluminium di-stearate .... 

Aluminium tri-stearate .... 

Per cent. 




170° C. 
157° C. 
115° C. 

Activated Alumina. Specially prepared activated alumina has found many uses, 
both in the United States and in Great Britain, as a desiccant for the removal of 
traces of moisture; for the adsorption of organic vapours ; for the removal of acids 
from oils, and as a catalyst. It has been made in Great Britain since 1940. Its great 
activity is claimed to be due to the presence of sub-crystalline y AI2O3.H2O of 
particle size between 100 and 150 A. 

The composition of activated alumina for use as a desiccant for packages is 
dealt with in British Standard Specification B.S. 2541 : 1960, which requires the 
material to consist of hydrated alumina free from extraneous matter and with a 
moisture content (loss on heating at 140-145°C.) not exceeding 2 per cent. The 
activated alumina, if granular, has to comply with the following particle size 

Residue on f in. mesh sieve 

Residue on i in. mesh sieve 

Passing 20-mesh sieve 

Passing 60-mesh sieve 

Passing 1 20-mesh sieve (after agitation in a prescribed manner) 

Per cent, 
10 max. 
0-5 max. 
01 max. 
0-2 max. 

The aqueous extract shall have a pH value between 5 and 8. Ammonia or 
ammonium compounds (calculated as NH3) not to exceed 10 p.p.m. ; water soluble 
chlorides (calculated as NaCl) 05 per cent. max. ; water-soluble sulphates (calcula- 
ted as Na2S04> 1 per cent. max. ; absorptive capacity as determined by a prescribed 
method must not be less than 10 per cent. 

Activated alumina has a greater affinity than any other commercial absorbent 
for moisture at very low dew points and finds use in drying refrigerant liquids such 
as Freon or methyl chloride. During World War II, it found considerable use in 
desiccant packages for precision instruments and in the air-conditioning of naval 
vessels and storage rooms containing material likely to be damaged by moisture, 
and their use continues. It is particularly suitable for drying gases such as hydrogen, 
carbon dioxide, nitrogen and the rare gases. As a catalyst it is useful for processes 
involving condensation, alkylation and dehydration. It is also employed in desul- 
phurizing petrol and coal distillates. 

Activated alumina can be repeatedly reactivated by heating to a temperature of 
about 100°C. above the boiling point of the liquid adsorbed, but its activity is 
destroyed by heating to about 800°C. 



Other Aluminium Compounds. The pigment known as " gloss white " consists of 
a mixture of aluminium hydrate and blanc fixe and is used as a base in the manu- 
facture of surface coating pulp colours for the printing ink industry. The pigment is 
commonly made by the interaction of solutions of alum, soda ash and barium 

Aluminium hydrate is used as a base on which dyestuffs may be fixed by pre- 
cipitation and in making colours and lakes for use in printing inks. 

" Alusil " is a form of synthetic hydrated aluminium silicate, produced by 
Joseph Crosfield & Sons Ltd. of Warrington, Lanes., for use as a reinforcing 
ingredient in natural or synthetic rubber mixings. It is a fine, white powder which all 
passes a 300-mesh B.S. sieve, the ultra-fine ultimate particles having a size of 
30-50 ntyi. It has a pore volume of 0-28 c.c./g., refractive index of 1-45, specific 
gravity 1 -95, oil absorption value (determined according to B.S. 1795) 180 per cent. 
w/w, loss on drying at 250°C. 140 per cent, and at 950 to 1,000°C. 180 per cent., 
surface area (nitrogen absorption) 170 sq. m./g. 

A ceramic fibre named " Fiberfrax " made by the Carborundum Company at 
Niagara Falls, New York, consists of about equal amounts of alumina and silica 
together with a small quantity of boric acid. The mixture is melted in an electric 
furnace and the molten product, on being subjected to a controlled blast of air, 
forms a cotton-wool-like mass of fibres up to 3 in. long and averaging 4 microns in 
diameter. It can withstand temperatures up to about 1,250°C. and does not soften 
until nearly 1,650°C. It is marketed in the form of blocks, non-woven blankets, or 
in bulk, and is stated to be useful as a packing material, particularly for expansion 
joints, and heat and electrical insulation. 

Alumina is an important constituent of certain porous ceramic media used in 
many chemical operations. One example is " Coralith," made by Aerox Ltd. of 
Glasgow. It consists of carefully graded fused alumina united by a vitreous bond 
having an affinity for alumina. The product, which is available in several grades with 
average pore size ranging from 5-7-5 microns up to 160-200 microns, is claimed to 
be suitable for many gaseous and liquid filtering operations, particularly where high 
temperatures are involved. 

A new industrial product, known as " Lucalox " has been developed by the 
U.S. General Electric Co. It is made by compressing fine grain, high purity 
aluminium oxide powder and then firing at a high temperature. Lucalox is almost 
as transparent as clear glass, resists extreme heat and can be fabricated to any 
desired shape. It is anticipated that the product will find use for electrical insulators, 
for transparent containers required to withstand high temperatures. 

Hydrous alu mini u m silicate is also sold for use as a rubber filler under various 
trade names such as " Aerofioated Paragon," " Aluminium Flake," " Par " and 
" Catalpo." Sodium-aluminium silicate, produced by Imperial Chemical 
Industries Ltd. is marketed under the name of " Fortafil A70 " for use as a white 
reinforcing rubber filler. 

A number of aluminium organic compounds have attracted attention in recent 
years and a useful summary of their actual and potential uses has been given by 
J. H. Harwood (1959). The formate and acetate have been fairly widely used in a 



number of waterproofing processes. Aluminium isopropoxide is used for water- 
proofing textiles, often in conjunction with paraffin wax. Aluminium alkyl com- 
pounds appear to have possibilities in fuels for rocketry. 

Aluminium naphthenate, oleate and palmitate are used as thickening and 
suspending agents in some paints. 

Other Uses for Bauxite 

Abrasives. Various abrasives are produced by the fusion of calcined bauxite or 
prepared alumina in an electric furnace. The calcined ore should carry 80-86 per 
cent. AI2O3, and may contain 4-8 per cent. Si02, 4-9 per cent. Fe2(>3 and 2-5 per 
cent. T1O2. For the production of a high-grade " artificial corundum " in the electric 
furnace, the highest grade of bauxite is required containing low percentages of silica 
and iron oxide. Occasionally, however, bauxites containing rather less than 50 per 
cent. AI2O3 and up to 10 per cent. Si02 and 15 per cent. Fe203 are used. Highly 
ferruginous bauxites are sometimes employed for the production of artificial 

The U.S. National Stockpile Specification P-5b of July 1st, 1948, requires 
bauxite for abrasive purposes to have the chemical composition shown in Table 10. 

Table 10 

Bauxite for Abrasive Purposes. U.S. National Stockpile Specification P-5b, 1st July, 1948 

Chemical Composition 

Per cent, by weight 
(calcined basis)* 

Alumina, AlaOst (min.) . 

Silica, SiOa (max.) ......... 

Lime, CaO (max.) ........ 

Magnesia, MgO (max.) . 

Total alkalis as oxides (max.) ....... 

Total iron as FeaOa (max.) 

Phosphorus as P2O5 (max.) ....... 

Manganese + chromium + vanadium as MnC>2, Cr2C>3, V2O5 (max.) 
Titanium as Ti02 (min.) 


* Sample to be dried at 105° C. and analysed in the dried condition including a determin- 
ation of combined moisture content. Dry basis assay to be converted to calcined basis by 
computation using the actual moisture determination, thus: 

„ , . , , . , . . per cent, by weight dry basis x 100 

Per cent, by weight, calcined basis = 100 _ per oeDt combined H 2 in dried samp le 

t Alumina shall be determined by difference using the " Tri-acid " method of analysis. 

Abrasive grade aluminium oxide has a hardness of over 9 on Mohs's scale, or 
10-1 1 on the Woodall scale, which is based on relative resistance to abrasion. It has 
a specific gravity between 3-9 and 4 and finds use principally in grinding wheels, 
coated abrasives and for polishing. The production of this abrasive in the United 
States has been around 200,000 short tons per annum, whilst Canada has had an 
annual output of about 163,000 short tons. 
The U.S. National Stockpile Specification P-90-RI of January 13th, 1953, for 



the purchase of crude aluminium oxide for abrasive purposes requires the material 
to be produced by calcining bauxite in an electric arc furnace for twenty-four 
hours. The material must contain a minimum of 94 per cent, alumina with the 
following percentage limits for other constituents: silica, 2; iron oxide, 0-75; 
titanium dioxide, 2-4; lime, 0-35. At least 99-7 per cent, of the material must be 
fully fused, of a greyish or reddish brown colour, have a conchoidal or irregular 
granular fracture, and contain less than 5 per cent, of mullite. The sintered, or only 
partially fused material, should not be more than 0-3 per cent. There should be no 
lumps over 6 in. and not more than 6 per cent, should pass a No. 60 U.S. standard 

Aluminous Cement. Bauxite is an essential ingredient for the manufacture of the 
product commonly termed " Ciment Fondu," aluminous or high alumina cement, 
which differs in many respects from ordinary Portland cement. In Great Britain the 
product is manufactured by the Lafarge Aluminous Cement Co. Ltd., and marketed 
under the name " Ciment Fondu." The manufacture of high alumina cement differs 
from that of Portland cement in that the raw materials, bauxite and chalk or lime- 
stone, are mixed together in dry lump form, melted in a reverberatory furnace at 
high temperature, the molten product cast into pigs, which are broken up and 
ground to a fine powder, without the addition of gypsum or any other product. 

Bauxite suitable for the purpose should have a minimum ratio of alumina/silica 
of about 10 : 1 and that of alumina/ferric oxide of about 2:1. The two ratios are not 
entirely independent, since a cement with a lower iron content can support a higher 
percentage of silica. 

The chief differences in chemical composition between Portland cement and high 
alumina cement lie in the fact that the principal constituent of the first named is tri- 
calcium silicate, which on mixing with water gives mono-calcium silicate and lime, 
whereas in the case of high alumina cement, the principal constituent is mono- 
calcium aluminate, which, on hydration, yields chiefly hydrates of calcium aluminate. 
Some mono-calcium silicate is also formed, but the amount of alumina is greatly 
in excess of that required to combine with the lime and so, finally, gelatinous 
alumina is liberated in excess. 

Typical analyses of Ciment Fondu and of Portland cement are shown, for 
comparison, in Table 11. 

Table 11 

Chemical Composition of Ciment Fondu and Portland Cement. 
Per cent. 

Ciment Fondu 

Portland Cement 

Silica, Si0 2 .... 

5 09 


Alumina, A1 2 3 .... 

39 04 


Ferric oxide, Fe a 3 



Ferrous oxide, FeO 

4 06 


Titanium dioxide, TiO a 



Lime, CaO .... 


63 04 

Magnesia, MgO .... 



Sulphuric anhydride, SO a 




Considerable variations are possible in the chemical composition of high 

alumina cement without changing its resultant characteristics, but it is specified that 

x . AI2O3 (per cent.) , ,, , , , , „ 

the ratio „ „ , should not be less than 0-85 or greater than 1 -3. 

CaO (per cent.) 

High alumina cements have a relatively slow setting time of approximately 2-4 
hours and are characterised by the rapidity with which they increase in strength 
after setting. They are also resistant to attack by many dilute acids, sulphurous 
gases, oils, mineral sulphates, sewage or seawater. 

Ciment Fondu, when mixed with a suitable aggregate, such as firebrick grog, can 
be used as a refractory concrete or mortar, which is stable and exhibits no apparent 
shrinkage up to 1,300° C. 

High alumina cement, as denned in B.S.I. Specification B.S. 915 : 1947, must 
not contain less than 32 per cent. AI2O3 and the ratio of the percentage of AI2O3 to 
CaO must not be less than 0-85 or more than 1-3. Tests are also specified for the 
compressive strength of cement-sand cubes; setting time and soundness of neat 
cement pats, and fineness. 

The Lafarge Aluminous Cement Company also manufacture a high-purity 
calcium-aluminate cement called " Secar 250," which is suitable for making super- 
duty refractory concretes able to withstand temperatures up to 1,800° C. if used with 
suitable aggregates. It approximates in chemical composition to tricalcium penta- 
aluminate and contains AI2O3 70-72 per cent., CaO 26-29 per cent., less than 1 
per cent, of silica or iron compounds and no titanium dioxide. " Secar 250," when 
mixed with water and refractory aggregates has a normal setting time (2-4 hours) 
and thereafter hardens with great rapidity. The maximum service temperature is 
1,800°C. when the aggregate is fused alumina and is lower when other aggregates 
are used, e.g. firebrick 1,450°C, fired kaolin 1,500°C, sillimanite 1,550°C, 
chrome 1,650°C, carborundum or brown fused alumina 1,700°C. Refractory 
concretes made with ' ' Secar 250 " are claimed to have high resistance to spalling, and 
attack by slag or products of combustion, very high cold strength and be ready for 
service twenty-four hours after placing or casting. 

Refractories. Bauxite has been used for lining rotary cement kilns and metal 
working furnaces where corrosion from basic metals may be anticipated. For such 
purposes a bauxite low in silica is preferred. The bauxite is usually calcined at a 
temperature between 1,300 and 1,400° C. before being moulded into firebricks. The 
fusion temperature of bauxite refractories varies between 1,600 and 1,900° C, accor- 
ding to the purity of the bauxite used. 

The U.S. National Stockpile Specification P-5c of December 5th, 1951, for 
refractory grade bauxite requires the material to be delivered in a calcined form and 
to have a minimum bulk density of 3-1. The following maximum percentage limits 
are also specified : silica, 7 ; iron oxide, 3 -75 ; titanium dioxide, 3 -75 ; loss on ignition, 
0-5. The content of alumina (difference between 100 and the total of the percentages 
of silica, iron oxide, titanium dioxide and loss on ignition) must not be less than 85 
per cent. 

Two interesting refractory alumina products made by Morgan Refractories 
Ltd. of Wirral, Cheshire, England, are " Purox " recrystallized alumina for which 



a maximum service temperature of 1,950°C. is recommended, and "Purox" 
sintered pure alumina suitable for temperatures up to 1,450°C. The crystal structure 
of the first-mentioned is obtained by heat treatment; the material is supplied as 
tubes, crucibles, bricks or special shapes. The pure sintered alumina is produced by 
firing at a lower temperature and is therefore not impervious. Both the above 
products contain 99-7 per cent. AI2O3. 

Oil Refining. An activated product made from a high grade bauxite is often 
employed for decolorizing and desulphurizing petroleum products, particularly 
kerosene and cracked spirit. The bauxite is usually ground to pass a 30- or 60-mesh 
screen. All bauxites are not equally effective for oil refining and the suitability of any 
particular bauxite can only be determined by practical trial. It would appear that 
the most promising bauxites are those which contain a high percentage of combined 
water; some Indian bauxites with 24 per cent, water give better results than French 
ore carrying only 12 per cent. Before use, the raw bauxite is activated by being 
heated to a suitable temperature — in some cases about 400° C. 


Alunite or alumstone is hydrated sulphate of aluminium and potassium having 
the formula, when pure, K2O.3AI2O3.4SO3.6H2O, corresponding with the follow- 
ing percentage composition: AI2O3, 37; K2O, 11-4; SO3, 38-6; and H 2 0, 130. 
Commercial samples frequently contain varying amounts of silica and small 
quantities of iron, and part of the potassium may be replaced by sodium. The pure 
mineral is white, but impure varieties may be coloured pink or red. The sources of 
supply are La Tolfa, Italy; New South Wales; South Australia; Utah, U.S.A.; 
Japan; Spain; and Southern Korea. 

No production of alunite in Australia has been recorded since 1952, when 314 
long tons was mined. Spain has recorded occasional production of alunite, 884 long 
tons in 1952, 553 long tons in 1953. In recent years Japan has produced increasing 
amounts of alunite, rising from 2,573 long tons in 1952 to 6,245 long tons in 1956. 

Uses. Alunite is insoluble in water or in the common acids, but on calcination at 
500°C. it loses water of hydration and gives a residue consisting largely of 
anhydrous potash alum, part of which is soluble in water or dilute acid. Calcination 
at about 750°C. releases most of the sulphur combined with the aluminium and 
gives a residue of potassium sulphate and alumina. 

Alunite has been used as a raw material for the manufacture of both potash 
alum and sulphate of potash, particularly during the two World-war periods. 

For certain processes used in the United States for treating alunite it is desirable 
that the mineral should contain as little sodium as possible. 


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Standard Specifications 

American Society for Testing Materials: 
A.S.T.M. Standards, 1958: 

Aluminium Pigments, Powder and Paste for Paints, D 962-49 

Aluminium Wire Conductors, B 230-58. 

Aluminium for Use in Iron and Steel Manufacture, B 37-49. 
British Standards Institution: 

Activated Alumina as a desiccant for Packages, B.S. 2541 : 1960. 

99 per cent. Primary (virgin) Aluminium notched bars and ingots for remelting. 4.L.3 1 : 1950. 

99-7 per cent. Primary (virgin) Aluminium notched bars and ingots for remelting. L.48 : 1950. 

Aluminium and Aluminium Alloys, ingots and castings. 1490-LM-O : 1949. 

Aluminium of 99-99 per cent, purity. B.S./STA7 A. 

Aluminium of 99-8 per cent, purity. B.S. 1470/SLB; B.S. 1471, TIB; B.S. 1474, WIB; B.S. 
1476, EIA; B.S. 1477, PIA. 

Aluminium of 99-7 per cent, purity. B.S./STA7-A2 ; B.S. 148. 

Aluminium of 99-6 per cent, purity. B.S./STA7-A3. 

Aluminium of 99-5 per cent, purity. B.S. 1470, SIB; B.S. 1471, TIB; B.S. 1474, WIB; B.S. 
1476, EIB; B.S. 1477, PIB. 

Aluminium of 990 per cent, purity. B.S. 3 L 16; B.S. 3 L 17; B.S. 4 L 31; B.S. 1490, LMO; 
B.S. L 49; B.S. 2 L 36; B.S. 134; B.S. 1470 SIC; B.S. 1470 TIB; B.S. 1474 WIC; B.S. 
1476 EIC; B.S. 1477 TIC; B.S./STA7 A4A, A4B, A4C, A4D, A4E. 

Leafing Aluminium Flake (powder and paste) for Paints. B.S. 388 : 1952. 
U.S. Dept. Commerce 

Aluminium Powder for Paints, T.T.— A.— 476 (1932). 

Aluminium Pigment for Paste, T.T.— A.— 466 (1932). 
U.S. Federal Specification: ,„,„ 

Aluminium pigment, powder and paste for paint. T.T.— A— 468a (Oct. 7th, 1949). 
U.S. National Stockpile Specifications: 

Aluminium pigmetal. P-62-RI. July 30th, 1954. 

Bauxite for Abrasive Purposes, P-5-B, July 1st, 1948. 

Bauxite for Metallic Aluminium. P-5a-R, August 19th, 1952. 

Bauxite for Refractory Use. P-5c, December 5th, 1951. 

Crude Aluminium Oxide for Abrasive Use. P-90-RI, January 13th, 1953. 



The most important ore of antimony is the sulphide, stibnite or antimony glance 
(SD2S3). Of less commercial importance are the oxides, senarmontite and valentinite 
(Sb203>, whilst the oxysulphide (kermesite) and the hydroxide (stibiconite) are 
worked in certain districts. 

Relatively large percentages of antimony are also present in certain complex 
sulphide ores, such as tetrahedrite (sulphide of copper and antimony containing up to 
29 per cent. Sb), jamesonite (sulphide of lead and antimony with 32 to 35 per cent. 
Sb) and bournonite (sulphide of copper, lead and antimony with 25 per cent. Sb). 
In such cases the antimony may be recovered as a by-product in smelting the ore for 
its lead or copper content. 

The complex sulphides usually occur associated with lead ores, but sometimes 
they constitute the principal ore mineral, as in the Dundas district of Tasmania. 
Tetrahedrite is the chief antimony-bearing mineral at the Broken Hill deposits in 
New South Wales. Stibnite deposits usually occur as veins in fissures, shears or 
joints or as irregular replacement deposits. 

As antimony metal has a marked solvent action on most other metals, its separa- 
tion from such metals is difficult and frequently quite uneconomic. Consequently, 
the smelter of antimony ores usually stipulates reasonably pure ores. Lead and 
arsenic are the commonest impurities but copper and zinc are much more deleterious. 
Iron, sulphur, and the general run of gangue (lime, silica, etc.) are not objectionable, 
except that they reduce the antimony content of the ore. In ore suitable for the 
production of metal containing 99-6 per cent, antimony and over, the ratio of 
impurities to antimony is important, the usual limits being: Pb, less than 0-1 per 
cent, of the Sb content of the ore; As, less than 0-2 per cent, of the Sb content of 
the ore, Cu, or Zn, less than 0-2 per cent, of the Sb content of the ore. 

A second grade ore suitable for the direct production of 99 per cent, antimony 
metal might be of the following composition: Sb, 40-65 per cent.; Pb, less than 
0-6 per cent, of the Sb content of the ore; As, less than 0-5 per cent, of the Sb content 
of the ore; Cu, or Zn, less than 0-5 per cent, of the Sb content of the ore. 

Lower grade ores are bought with either the lead or arsenic up to 2 per cent, of 
the antimony content of the ore, but such ores require special refining and so carry 
a heavy penalty. In the case of lead, a metal containing up to 10 per cent, lead is 
sometimes produced, and sold at largely reduced prices. 

Payment for antimony ore is usually made on a sliding scale per unit of antimony, 
with deductions for certain metals, such as lead, copper, zinc and arsenic if present 
over an agreed percentage. Thus, in lump ore containing 45 to 50 per cent, of 
antimony, 01 per cent, of arsenic may be allowed to be present without penalty, but 
each 1 per cent, in excess of this amount may involve a deduction from the price 
paid for each unit of antimony. 

The grade of the antimony ore or concentrates treated varies considerably with 
the country and commercial conditions prevailing at the time. Thus, in the United 
States, the average percentage of antimony in the mineral treated in the years 
1944-1948 was 35 1, 12-9, 17-9, 26-6 and 400 respectively. 



World Production 

The world's production of antimony from ore, like that of many other minerals, 
rose considerably during World War II, the peak year being 1942, with an estimated 
total of 49,800 long tons as compared with 38,200 long tons in 1939. In 1951, the 
world's production was about 61,000 long tons (in terms of metal) but this had fallen 
to about 33,000 long tons in 1953. By 1956 it had risen to 47,000 long tons and in 
1958 totalled about 39,000 long tons. About one-fifth of the world's production of 
antimony concentrates comes from the Union of South Africa where the Consoli- 
dated Murchison Gold Mine in the Transvaal treats a gold-antimony ore and ex- 
ports antimony concentrates containing about 63 per cent, of the metal. The other 
large producing countries are China, Bolivia, Mexico, Yugoslavia, Czechoslovakia, 
Turkey, Algeria, Peru and Australia. 

In addition to antimony produced direct from the ore, considerable quantities 
of secondary antimony are recovered from scrap, such as old storage battery plates, 
grids and sludge. No detailed world statistics are available for secondary antimony 
recovery, but the quantity is considerable, as is evidenced by the fact that for some 
years past the United States has recovered about 20,000 long tons of secondary 
antimony annually. 

In 1958 in the United Kingdom the consumption of antimony in scrap was 
4,224 long tons in antimonial lead and 244 long tons for other uses. 

No antimony ore is produced in Great Britain, trade requirements being met by 
imports of ore and concentrates which, in 1958, amounted to 11,274 long tons. 
Most of the imports came from the Union of South Africa and Bolivia, with smaller 
amounts from Chile and Peru. 

Smelting Antimony Ore 

Methods used for the extraction of antimony from its sulphide and oxide ores 
vary with the grades of ore treated and may be grouped in five main classes, all of 
which are " dry " methods. 

(1) Volatilization processes for ores carrying from 15 to 25 per cent, of the metal, 
as employed in France, Yugoslavia, China, Italy and elsewhere. When antimony 
sulphide is roasted at temperatures below 500° C. with controlled admission of air, 
it is converted to the volatile trioxide, SbaOs, which is condensed in a special plant. 

(2) Blast-furnace methods for ore carrying from 25 to 45 per cent, of the metal, 
used in the United States, England and Mexico. The ore is smelted with a mixture 
of coke, limestone and some form of iron oxide, often an iron slag. 

(3) Ores carrying from 45 to 60 per cent, of the metal may be liquated for the 
production of antimony sulphide, often termed " crude antimony." The operation 
is carried out by heating walnut-size pieces of ore at 550-600° C, either in crucibles 
or reverberatory furnaces, by which means a large proportion of the sulphide is 
melted and can be separated from the associated gangue. The operation has to be 
carried out in a reducing atmosphere so as to avoid the formation of the volatile 
antimony trioxide. The residue from the liquation process, which contains from 
15 to 20 per cent, of antimony sulphide, can be treated by the volatilization process. 



(4) Ores containing about 50 per cent, of the metal as sulphide can be treated by 
direct reduction. 

(5) Mixtures of sulphide and oxide ores are usually treated by blast-furnace 

As the percentage recovery of crude antimony decreases very rapidly with the 
proportion of gangue present in the ore, the treatment of very low grade ore is 

The U.S. National Stockpile Specification P-2b, dated June 29th, 1950, for the 
purchase of chemical grade antimony sulphide ore suitable for the production of 
antimony oxide requires the mineral to be in lumpy or flaky condition, not over 10 
per cent, of which will pass a i-in. screen. The product should contain a minimum of 
60 per cent, of antimony, with not less than 22 per cent, of combined sulphur and not 
over 0-5 per cent, of lead (Pb) and arsenic (As). 

The U.S. National Stockpile Specification P-2c, dated June 29th, 1950, for the 
purchase of liquated antimony sulphide suitable for the manufacture of primers for 
small-arms ammunition, requires a minimum of 69-3 per cent, antimony, and 23 
per cent, total sulphur. The following maximum percentages are also specified: 
lead, 0-15; iron, 1-3; free sulphur, 0-25; moisture, 0-2; acidity, 001. The insoluble 
residue should not normally exceed 1 per cent., but may be up to 3 per cent, if the 
lead does not exceed 001 per cent, and iron is not over 01 per cent. 

Reduction to Metal. Most of the metallic antimony of commerce is produced by 
the reduction of either the sulphide or the oxide, only a small quantity being ob- 
tained by the direct smelting of the sulphide ore. 

The reduction of the sulphide is usually made by converting to the oxides and 
reducing in a reverberatory furnace. The English Precipitation method, which 
involves smelting with iron as a reducing agent, has practically gone out of use. 

The crude metallic antimony obtained by either process usually contains 
sulphur, iron, arsenic, copper and lead, and needs refining. With the exception of 
lead, all these impurities can be removed by fusion with suitable oxidizing and 
slagging agents. 

In 1956 a new process was announced for upgrading cathode antimony by the 
Sunshine Mining Company of Coeur d'Alene district, Idaho. The cathode metal is 
mixed with flake caustic soda and heated for three hours at about 590° C. in an iron 
pot in an electric furnace. The resultant cake is leached with water and yields a 
metal containing less than 0-05 per cent, impurity. In 1957 it was announced that 
two United States and one British company were producing super-purity antimony 
suitable for use in the production of electronic intermetallic compounds. Semi- 
conductors now being developed commercially include antimony-iridium and anti- 
mony-aluminium. The latter has essentially the same crystal structure as germanium, 
responds in a similar way electrically and has photoelectric properties. Super- 
purity antimony (99.999 per cent.) is being produced in Great Britain in commercial 
quantities by Associated Lead Manufacturers Ltd. of Newcastle-upon-Tyne. 

An electrolytic process for extracting antimony from argentiferous tetrahedrite, 
which is not amenable to the usual treatment processes, is in use in the United States. 
Antimony is dissolved from the ore by means of a concentrated solution of sodium 



sulphide and the resultant solution of sodium thioantimonate is electrolysed in an 
anode diaphragm cell, using mild steel anodes and cathodes. 

The impurities present in several brands of commercial antimony are shown in 
Table 12. It has long been a trade practice to judge the purity of ingots of antimony 
by the development of a fernlike structure or " stars " on their surface. Actually this 
does not indicate the relative purity of the metal, as it largely results from cooling 
the molten metal under special conditions — usually under a slag having a lower 
melting point than the metal. 

Table 12 

Impurities in Antimony. Per cent. 






99-6 metal 

99 metal 

C. T. 

Lead, Pb. . 

< 004 0-6 




Tin, Sn 




Arsenic, As 

< 004 0-2 




Copper, Cu 

< 003 003 




Iron, FejsOs 

< 005 010 




Sulphur, S . 

< 005 005 

Some of the physical properties of pure metallic antimony are as follows : 

Atomic number 

Atomic weight 

Melting point 

Boiling point . 

Density (at 20° C.) 

Thermal neutron cross-section absorption 

Crystal structure . . 

Electrical resistivity (at 20° C.) 

Coefficient of linear thermal expansion (at 20-60' 

Young's modulus of elasticity 

Poisson's ratio 




630-5° C. 

1,440° C. 

6-68 g./c.c. 

5 barns 


41 -7 microhms/cm. 

8-5-10-8 X 10- 6 /° C. 

7-8 x 


Table 13 

A.S.T.M. Standard for Ingot Antimony, B 237-52 

Grade A 

Grade B 

Arsenic, max. ...... 

Sulphur, max. ...... 

Lead, max 

Other elements (iron, copper, nickel, tin, 
silver), each max. ..... 

Antimony (by diff.), min 

Per cent. 


Per cent 




A.S.T.M. standard B 237-52 for metallic antimony in ingot form requires the 
metal to have been made from ore, or other materials, by processes of reduction 
and refining. The requirements in regard to chemical composition are shown in 
Table 13 (see p. 33). 

The above requirements are the same as those of the U.S. National Stockpile 
Specification P-2a-R dated July 9th, 1956 for the purchase of antimony metal for 
making antimonial lead or battery metal. 


Antimony is chiefly used in the metallic form as a component of lead alloys, such 
as type and anti-friction metals, fusible alloys, electric storage battery plates and 
cable coverings. 

Table 14 
United States: Industrial Consumption of Primary Antimonyf 

Antimony Content in 

Short Tons 


to 1952 








Metallic Products : 

Ammunition . 








Antimonial Lead 








Bearing Metal . 








Cable Coverings 








Castings .... 








Collapsible Tube and Foil . 








Sheet and Pipe . 








Solder .... 








Type Metal 








Other .... 








Total Metallic Products 








Non-metallic Products: 

Ammunition Primers 
















Flameproofing Chemicals . 








Ceramics and Glass . 








Matches .... 
















Plastics .... 








Rubber Products 








Other Products. 








Total Non-metallic Products 
















* Data not comparable with following years. 

t From " Minerals Yearbook," U.S. Bur. Mines. In 1957 consumption components 
were reclassified and figures for previous years have been revised to make all quantities 
in the table comparable. 

t Included with other. 



A useful indication of the relative consumption of antimony in the United 
States for a number of industrial purposes is given in Table 14, and for Great 
Britain in Table 15. 

Table 15 

United Kingdom : Consumption of Antimony Metal and Compounds.* 
In terms of Antimony Metal 

Long tons 






Other Antimonial Lead 

Miscellaneous uses .... 
For White Pigments .... 

For other uses 

Sulphides, including crude 

















Total consumption of Antimony Metal 





* From Bulletin, British Bureau of Non-ferrous Metal Statistics, Birmingham, England, 

Metallic Antimony. An important use for metallic antimony is for hardening lead 
to be used for storage battery plates; the lead-antimony alloy used may contain 
between 6 and 12 per cent, of antimony. About three-quarters of the old battery 
plates are re-treated for the recovery of their lead content, but after recovery, the 
lead contains only about 4 per cent, of antimony and so further antimony must be 
added to make the recovered metal usable for new plates. In the refining process, 
much of the antimony is removed in the furnace skimmings, the re-smelting of 
which gives a " hard lead " with up to 16 per cent, of antimony. 

Considerable quantities of lead, hardened with about 1 per cent, of antimony, are 
used for sheaths for telephone and other cables. 

Collapsible lead tubes may contain up to 4 per cent, of antimony, added for 
hardening and strengthening, but 2 per cent, is more general. 

Antimony is an important component of certain low-melting alloys, to which 
reference is made in the chapter dealing with Bismuth {see p. 87). It is a useful 
constituent of standard varieties of type metal on account of its slight expansion on 
solidifying, which gives a sharp outline to the type. 

The chemical compositions of various classes of type metal, as specified in 
B.S./STA7, are shown in Table 16. 

Lead sheet and pipe, used for roofing and gutters in the building trades, usually 
contains about 6 per cent, of antimony. 

For some purposes in chemical plant, where the usual high purity metal would be 
too soft, lead is sometimes used containing between 1 and 1 2 per cent, of antimony. 

c 2 



Table 16 

Composition of Type Metal, B.S.jSTAl. Per cent. 




Lead, Pb 

Tin, Sn 

Antimony, Sb 

Other elements .... 








* Copper, iron and arsenic not to exceed 0-05 per cent. each. 

Such antimonial lead, however, has less resistance to corrosion than has ordinary 
chemical lead. 

Two promising antimonial semi-conductors, which may be commercially deve- 
loped in the near future, are indium-antimony and aluminium-antimony. Indium 
antimonide made for use in electronics by the Consolidated Mining and Smelting 
Co. of Canada has an impurity tolerance of about one part in 10 million. 

Antimony Compounds. These have many uses in industry. The crimson sulphide 
and golden sulphide are used as pigments in the rubber industry, which is the sole 
use apart from a small quantity of golden sulphide for medicinal purposes. Anti- 
mony trioxide — the only oxide produced commercially — is used as a pigment in the 
paint and enamel industries, as an opacifier for vitreous enamels and also as one of 
the constituents of certain optical glasses. Sodium antimoniate is also used as an 
opacifier in vitreous enamelling. Crude antimony (black liquated trisulphide) is 
used on the striking surface of safety match-boxes and in the detonating caps for 

In recent years antimony compounds have been increasingly used as flame- 
proofing agents for textiles, considerable impetus having been given during World 
War II to research designed to meet military requirements. The use of antimony 
oxide as a flame retardant in polymers, such as P.V.C., and paint, has been 
developed more recently. One process, developed by Associated Lead Manufac- 
turers, Newcastle-upon-Tyne, employs their " Timonox " brand of white, finely 
divided antimony oxide, SbaOs, in conjunction with an emulsion of a chlorinated 
organic compound, such as polyvinyl chloride or chlorinated paraffins, which 
decomposed by heat will yield hydrogen chloride. This, in turn, reacts to produce 
antimony chloride, a good flame-retarding agent. It is claimed that textiles so 
treated can withstand laundering or dry cleaning during the normal expectation of 
life of the garment. P.V.C. compounded with antimony oxide is suitable for flame 
resistant belting for use in coal mines. Most paints can be made flame-retardant by 
replacing part of the pigment by antimony oxide. Another flame-proofing compound 
for textiles, marketing as " Lifeguard " by Peter Spence Ltd. of Manchester, is 
based on a combination of oxycompounds of antimony and titanium. This process 
is unique in that it is based on the precipitation in the fibre of an oxycompound of 
titanium together with the antimony oxide. 

Other flame-proofing compounds containing antimony include a mixture of 



oxychlorides of antimony and titanium, known as " Erifton 573," and a mixture 
of antimony oxychloride and titanium dichloracetate marketed as "Titanox 

In another process antimony chloride, SbCk, dissolved in an organic solvent, is 
used to impregnate fabrics which have been previously treated with a solution 
of sodium carbonate and dried. 

Most chemical manufacturers in Great Britain use antimony metal as the 
starting point for the production of the oxides and salts of antimony, and for these 
purposes require a product containing over 99 per cent. Sb with only traces of iron, 
arsenic, sulphur, copper and lead. One user specifies a metal containing not more 
than the following percentages of impurities: As, 01; Fe, 0-3; S, 0-3, and only 
traces of copper and lead. 

British Standard Specification B.S. 338 : 1952 for antimony oxide for use in paints 
requires it to contain not less than 99 per cent, of antimony expressed as its oxide, 
Sb 2 03, calculated on the product after drying at 98°C. Matter volatile at 98 to 
102°C. must not exceed 0-5 per cent, and the residue not passing a 240-mesh sieve 
is limited to 0-25 per cent. Matter soluble in water must not exceed 0-4 per cent, and 
the acidity or alkalinity of the aqueous extract must not exceed 01 per cent., 
calculated as H2SO4 or Na2C03, on the original material. 

Manufacturers of antimony compounds for pharmaceutical use require a high- 
grade metal with the following maxima for impurities: arsenic, 001 per cent.; lead, 
0-3 per cent. ; and iron, 0025 per cent. 


" Strategic Mineral Supplies." By G. A. Roush. Lond., 1939, 485 pp. (Antimony, pp. 238-273). 
" Antimony Pigments." By J. A. Fredrickson. " Protective and Decorative Pigments." Ed. by 

J. J. Mattiello. Lond., 1942, Vol. 2, pp. 418-426. „.„.,„ 

" Antimony: Its Metallurgy and Refining in Recent Years." By C. Y. Wang and G. C. Riddell. 

Trans. Amer. Inst. Min. Met. Eng. (Reduction and Refining of Non-ferrous Metals), 1944, 

159,446-461. ,. . 

" Outlines of Paint Technology." By N. Heaton. 3rd Ed., Lond., 1947, 448 pp. (Antimony, 

pp. 88-90.) 
" Antimony Smelting." By W. Wendt. Metal Ind., 1948, 73, 303-305 and 329-330. 
" Antimony Production." By W. H. Dennis. Mine and Quarry Engng., 1949, 15, 289-296, diagrams 

and flowsheets. „,,.,. 

" Antimony, Materials Survey." Compiled for the Materials Office of the National Security 

Resources Board by the U.S. Bureau of Mines in co-operation with the Geological Survey. 

Washington, D.C., 1951, 264 pp. ^ xr 

" Antimony: Its Geology, Metallurgy, Industrial Uses and Economics. By C. Y. Wang. 3rd Ed. 

Lond., 1952, 170 pp. 
" Flame-proofing Textile Fabrics." By R. W. Little. New York, 1947 (Antimony p. 77). 
" Flame-proofing Textiles." By F. Ward. /. Soc. Dyers and Col., 1955, 71, 575-578. 
" Flame-proofing of Textile Fabrics with particular Reference to the Function of Antimony 

Compounds." By N. J. Read and E. G. Heighway-Bury. /. Soc. Dyers and 

Col. 1958, 74 (Dec.), 823-829. j r _, w , 

" Timonox as a Flame-retardant in Polymers and Paint." Associated Lead Manufacturers Ltd., 

Newcastle-upon-Tyne, 13 pp. 
" Antimony." By Pierre Bothorel, Nouveau Traite de la Chimie Minerale, Ed. by P. Pascal. 

Paris, 1958, Vol. XI, pp. 495-664. tt 

" Antimony." By H. N. Callaway. " Mineral Facts and Problems. U.S. Bur. Mines, Bull. 585 

(preprint), 1960, 9 pp. 
" Antimony." U.S. Bur. Mines Minerals Yearbook. (Annual). 


American Society for Testing Materials 
A.S.T.M. Standards, 1958. 

Metallic Antimony, B 237-52 



British Standards Institution : 

Antimony Oxide for Paints. B.S. 338 : 1952. 

Soft Solders. B.S. 219 : 1959. 

Type Metal. B.S. STA/7. 
U.S. National Stockpile Specifications : 

Antimony Sulphide Ore (chemical grade suitable for the production of antimony oxide). 
P-2b, June 29th, 1950. 

Liquated Antimony Sulphide (for use in the manufacture of primers for small arms ammu- 
nition). P-2c, June 29th, 1950. 

Antimony Metal (for national blends of antimonial lead). P-2a-R, July 9th, 1956. 


Although a number of arsenic minerals are known, such as arsenopyrite (FeAsS); 
orpiment (AS2S3); and realgar (AS2S2), commercial supplies of arsenic are obtained 
almost entirely as a by-product from the gases evolved during the roasting of metallic 
ores containing arsenides or sulpharsenides, particularly those of lead, copper, gold 
and tin. The name arsenic should be reserved for the metallic element, but in 
commerce it is frequently used to designate arsenious oxide, AS2O3, or white arsenic, 
a practice which is followed in this chapter. 

World Production 

The countries which marketed the largest quantities of white arsenic (AS2O3) or 
arsenical ores in 1958 were Sweden, the United States, France, Mexico, Belgium, 
Japan, Canada, Italy, Portugal, Southern Rhodesia and Brazil. 

During World War II, some countries, such as the United States and Mexico, 
more than doubled their output of arsenic, and a newcomer, Peru, attained an output 
of 6,800 long tons in 1944, but the production has since been negligible. Statistics of 
arsenic production are not complete, but the world's output marketed probably 
amounts to about 42,000 long tons per annum. The output of arsenic attainable 
from the Boliden gold mine in northern Sweden greatly exceeds market require- 
ments as the ore carries about 10 per cent, of AS2O3; much of the arsenic extracted is 
either stored or mixed with concrete and dumped into the sea. 

Most of the white arsenic recovered in the United States is obtained during the 
smelting of copper and lead ores, such as at Butte (Montana) and Tintic (Utah). The 
production of arsenic in Canada increased considerably during World War II, 
being obtained principally in the treatment of gold and lead ores. The output in 
1958 was 1,037 long tons. 

Only small quantities of white arsenic and arsenical soot are recovered in Great 
Britain, usually less than 100 long tons per annum, and hence the demands of 
industry have to be met by imports which in recent years varied considerably, the 
total for 1958 being 6,873 long tons. 

The country consuming the largest quantity of arsenic is the United States, 
which normally augments her domestic production by imports; in 1958 her apparent 
consumption of white arsenic was 18,300 long tons. 



Refining Arsenical Dust 

All the white arsenic of commerce is obtained by treating the arsenical soot which 
condenses in flue dust collecting systems and chimneys during the roasting of ores 
containing arsenic. As arsenious oxide or white arsenic begins to condense at a 
temperature of about 218 C C, it collects mainly in the cooler parts of the flue 
system. Lead-baghouse products containing 30 per cent, of white arsenic, and 
copper furnace and roaster dusts carrying from 20 to 30 per cent, are not uncommon. 
Various processes are in use for refining the crude arsenical dust. One of these is to 
roast the dust on the hearth of a Brunton furnace, previously adding a small 
quantity of sulphide ore — e.g. pyrites — to prevent the formation of non-volatile 
arsenites in the residue from the roast. The gases from the furnace are passed through 
a series of chambers in which white arsenic of 90 to 95 per cent, purity condenses. 
This crude white arsenic is further purified by being resublimed from reverberatory 
furnaces operating at about 550° C. so as to obtain a product of over 99 per cent, 

The American Smelting and Refining Co. of New York is producing arsenic of 
99-999 per cent, purity to meet the growing demand for such material as a 
component of some special low-melting glasses and for use in semi-conductor 
compounds. The arsenic contains less than 1 p.p.m. copper and a total of 1 p.p.m. 
of selenium, sulphur and halogens. 


The principal use for arsenious oxide is in the manufacture of insecticides, 
sheep-dips, wood preservatives, anti-fouling paint for ships, weed killers, in glass 
manufacture, as a constituent of some vitreous enamels and in the chemical de- 
barking of pulpwood. Small quantities of metallic arsenic are used in metallurgy. 

An indication of the relative quantities of arsenical compounds consumed by 
various trades is afforded by the statistics issued by the United States Bureau of 
Mines. In 1957, the amount sold as insecticides comprised 6,076 short tons of lead 
arsenate, 9,763 short tons of calcium arsenate, but the quantity used in " Paris 
Green " was not stated. Wood preservatives, in the form of " Wolman Salts " con- 
taining 25 per cent, of sodium arsenate, accounted for 987 short tons, whilst the 
amount of zinc meta-arsenate used for the same purpose is not stated. The corre- 
sponding figures for arsenic used in drugs are riot published, but may have totalled 
about 4,701 long tons. 

Calcium arsenate can be made by the process developed by the U.S. Depart- 
ment of Agriculture in which arsenic trioxide is oxidized to the pentoxide by means 
of nitric acid, the solution neutralized with caustic soda to form sodium arsenate and 
from this calcium arsenate is precipitated by adding milk of lime. 

Lead arsenate can be made by fusing white arsenic with caustic soda or a mixture 
of soda ash and sodium nitrate, dissolving the melt in water and adding a solution of 
lead nitrate, or acetate, so as to precipitate lead arsenate. 

Insecticides and Weed Killers. These uses account for about 70 per cent, of the 
world's consumption. Arsenic compounds are widely employed as insecticides and 



fungicides, often in the form of calcium arsenate, calcium arsenite, lead arsenate or 
Paris Green (copper acetate and arsenic). The form often favoured for combatting 
the boll weevil in cotton cultivation is calcium arsenate, the consumption being 
about 5 lb. per acre of plants. In recent years some consumers in the United States 
have changed over to organic pesticides. Arsenical weed killers usually consist of 
sodium arsenite which is also the form in which arsenic is used in sheep and cattle 
dips and for grasshopper bait. 

Insecticide makers usually require a free-running product of fine particle size 
containing 98 per cent, or over of AS2O3 and only traces of antimony. Makers of 
weed killers require a white product of not too fine particle size. 

Pulpwood Industry. The application of chemicals to living trees to facilitate bark 
removal is being used to an increasing extent in the pulpwood industry. Sodium 
arsenite injected into the tree during the sap-peeling season causes the tree to die 
and the bark to loosen after a few months. 

" Tanalith C," a copper-chrome-arsenic compound is used as a timber pre- 
servative. Its composition is given in A.S.T.M. Specification D1034-50 (see under 
"Chromium "p. 131). 

Wood Preservation. Fair quantities of arsenic, in various forms, are used for the 
preservation of telephone poles, mine timbers and railway sleepers. 

Glassmaking. It has been estimated that about 25 per cent, of the white arsenic 
consumed in the United States is used in the manufacture of opal and opalescent 
glass. White arsenic is sometimes used as an oxidizing agent in glassmaking to 
overcome the greenish colour caused by iron compounds. 

The glass industry usually requires a white arsenic containing 96 to 99-5 per 
cent. AS2O3, and has a preference for a dense product of fairly coarse particle size, 
but the iron content must be low. 

Other Uses. Arsenic oxide is used to a small extent in medicine as potassium 
arsenite and Erlich's "606"; and in preservatives for treating animal hides. 
Arsenic trisulphide crystals are used as a window material in some infra-red 

Metallurgy. The metal can be produced by heating a mixture of white arsenic 
and charcoal in a closed gas-fired furnace and condensing the volatilized metal. 

Probably, the most important use for metallic arsenic is as an addition to copper 
to increase its resistance to corrosion and erosion. Arsenical copper is much used 
in Europe for locomotive firebox stays and plates but, in the United States, steel is 
often preferred for the purpose. Arsenical copper is also used in motor car radiators 
and similar copper parts which have to be assembled by soldering, since arsenic 
raises the annealing temperature so that the plates do not lose strength. 

Crystal rectifiers made of arsenic-tellurium alloys are said to be less costly to 
manufacture than other metallic rectifiers and to be capable of withstanding 
exceptionally high electric voltages and currents. 

Metallic arsenic is sometimes added to lead shot to the extent of about 0-4 per 
cent, to assist in the formation of truly spherical pellets. The metal has also been 
added to solder, and is a useful component of lead-base alloys used for electric 
storage battery grids. 




" Arsenical Pyrites." By C. C. Downie. Min. J. (Lond.), 1943, 220, 128-9 (Metallurgical treat- 
" Production of Arsenic Trioxide at Anaconda." By L. V. Bender and H. Goe. Trans. Amer. Inst. 

Min. Met. Eng., Vol. 106, pp. 324-328. 
" Arsenic." By W. C. Smith. " Handbook for Non-ferrous Metallurgy." Ed. by D. M. Liddell. 

2nd Ed., 1945, pp. 94-103. 
" Production of Copper Arsenites." By P. Miller. Industr. Engng. Chem., 1947, 39, 1521-1530. 
" World Production of Arsenic: Its Application and Uses." Anon. 5. Afr. Min. Engng. J., 1947, 

58, 265-267. 
" Chemistry and Use of Insecticides." By E. R. de Ong. New York, 1948. (Arsenic compounds 

pp. 10-40, including bibliography.) 
" Arsenic." Encyclopedia of Chemical Technology. Ed. by R. E. Kirk and D. F. Othmer. Vol. 2, 

pp. 113-132. 
" Producing Peeled Pulpwood by Chemical Debarking." College of Forestry (Syracuse), State 

University of New York, 1955, 4 pp. 
" Arsenic." By Roger Dolique. Nouveau TraitS de Chimie Minerale, Ed. by P. Pascal. Paris, 

1958, Vol. XI, pp. 1-494. 
" Arsenic." By A. D. McMahon. " Mineral Facts and Problems." 17.5. Bur. Mines Bull. 585, 

1960 (preprint), 6 pp. 
" The Radio Chemistry of Arsenic." By H. C. Beard. Nuclear Science Series Nas — Ns3O03, 

National Academy of Sciences, Washington, D.C., U.S.A., 1960, 27 pp. 
" Arsenic." Minerals Yearbook. 17.5. Bur. Mines, (Annual). 


The name asbestos is used commercially to designate the fibrous varieties of about 
half-a-dozen silicate minerals which are characterized by the strength and flexi- 
bility of their fibres, and their resistance to heat. The most important of these are: 
chrysotile, crocidolite, amosite, anthophyllite, tremolite and actinolite. Each has its 
own field of utility, but the first three are the most important. 

Asbestos occurs in nature in three general types, known respectively as (a) 
cross fibre, (b) slip fibre, and (c) mass fibre. Cross fibre asbestos is the most important 
as it yields better fibres. The fibres are found at right angles to the walls of the vein 
in which they occur and may have a length up to 3 inches. Slip fibres occur more or less 
parallel to the rock faces between which they occur. The fibre may be as long as that 
in cross veins but, after separation, is usually of inferior strength owing to the 
more drastic dressing operations necessary to separate it from the rocky matrix. 
Mass fibre, as the name implies, occurs in masses rather than in veins, with the 
fibres often interlaced and not evenly orientated. It is the least important of the 
three types. 

It is generally considered that in order for an asbestos deposit to be worked at a 
profit, 4 to 6 per cent, of saleable fibre should be extractable from the rock sent to 
the mill. Under rather exceptional circumstances, however, a yield of 2\ per cent, 
has proved economic. 

Chrysotile, or serpentine asbestos, is a hydrated silicate of magnesium which 
approximates in composition to the formula H4Mg3Si209, but usually contains 
small percentages of iron oxide and alumina. In the mass, the mineral has a greenish 
colour but the separated fibres appear white. It is characterized also by the fineness, 



flexibility, silkiness and strength of its fibres, physical properties which render it 
very suitable for spinning or weaving. It will stand a fair degree of heat without 
breaking down or fusing, but when heated to above 450°C. it loses water and be- 
comes brittle. It is attacked easily by weak acids and by continued exposure to salt 
water. The best grades, when low in iron, are good electrical insulators. Chrysotile 
from Southern Rhodesia is outstanding in regard to its low content of iron and is 
therefore of special value as an electrical insulatory material, particularly for cables 
for use aboard ship. 

Crocidolite, or blue asbestos, is a member of the amphibole group and approxi- 
mates in composition to the formula H2Na2Fe5Sis024, but usually contains a small 
percentage of magnesia and a little lime. It has a characteristic blue colour, both in 
the mass and when fiberized. 

Blue asbestos, which is obtained almost entirely from the Cape Province and 
Transvaal in South Africa, usually occurs in cross-fibre seams interbedded in 
banded sedimentary ironstones. The width of seam varies, but rarely exceeds 3 
inches, most being i to 1 inch wide. 

Blue asbestos is rather more harsh than chrysotile and more difficult to weave 
into textiles, but usually possesses greater tensile strength and has the advantage, 
for some purposes, of being much more resistant to acids and some other chemicals. 
It is also more readily fusible than chrysotile. Being harsh in texture, and therefore 
rather abrasive, it is seldom used for packing and jointing purposes, except for 
special acid-resisting work. Its main use is as an insulator and in asbestos cement 

Amosite is considered to belong to the amphibole group of minerals but, from 
the standpoint of chemical composition, it closely resembles crocidolite. It is found 
in South Africa under similar conditions to blue asbestos and in the same type of 
rock, but it is usually greyish in colour and has much greater length of fibre, which 
is commonly 4 to 7 inches, but sometimes reaches 12 inches. 

This variety of asbestos has good flexibility and tensile strength, its resistance to 
heat is much greater than that of blue asbestos and it is but little attacked by acids. 
The fibres are relatively harsh and somewhat brittle, and hence it is rather difficult 
to spin, and is mainly used for insulating work, felts, sheets and sections, as well as 
in asbestos-cement products. 

Anthophyllite, another member of the amphibole group, has a composition 
which may be expressed by the general formula Mg7(Si 4 On) 2 (OH) a in which 
aluminium may replace magnesium or silicon and ferrous iron may replace 
magnesium, and is usually found in altered basic igneous rocks. It commonly occurs 
as a mass fibre and occasionally as slip-fibre. It is brittle and lacking in tensile 
strength and, usually, it cannot be spun. It is used chiefly in boiler coverings, fire- 
proof paints and occasionally in asbestos-cement goods. 

Tremolite, a silicate of magnesium and calcium, is usually found as long, white, 
silky fibres which lack strength and so are unsuitable for spinning. It is sometimes 
used for boiler insulation and is of interest from the chemical point of view as its 
freedom from iron compounds and resistance to acids renders it particularly suit- 
able for nitration purposes. 



Actinolite. A silicate of magnesium and calcium with some iron. It is of little 
commercial importance. 

The physical properties of the three principal asbestos minerals of commerce are 
summarized in Table 17. 

Table 17 

Asbestos Minerals* 





Fibre length (usual maximum) . 

11-2 in. 

1J-3 in. 

7 in. 

Tensile strength 


Higher than 


Flexibility .... 




Fineness of fibre 

Very fine 



Resistance to heat . 

Good, but 

Poor: fuses 

Good, but 

becomes brittle 

to a glass 

becomes brittle 

Resistance to acids, alkalis and 

sea-water .... 




Electrical insulating value 

Fair to good 



Heat insulating value 


Good for 
moderate heat 


Spinnability .... 




* From Non-Metallic Minerals. By R. B. Ladoo and W. M. Myers, 1951, p. 52. 

The commercial varieties of asbestos differ considerably in their resistance to 
chemical reagents. Chrysotile is essentially a basic magnesium silicate, Mg : Si, 1 : 1, 
i.e. it has an excess of MgO over the chemically equivalent amount of silica and 
hence its resistance to attack by acid is poor. Strong mineral acids dissolve out all 
the magnesia, leaving pure silica, the material retaining its original shape but having 
practically no strength. 

In crocidolite the basic constituents and silica are in nearly chemically equivalent 
proportions and its acid resistance is good. Amosite is slightly inferior to crocidolite, 
but much superior to chrysotile. 

Some interesting figures regarding the behaviour of the various types of asbestos 
towards certain acids and alkalis have been given by M. S. Badollet, a selection from 
which is given in Table 18. 

Table 18 

Solubility of Asbestos in Acids and Alkalis* 



Acetic Acid 




Actinolite .... 

Amosite .... 




Tremolite .... 






















* Per cent, loss in weight after refluxing for two hours in 25 per cent, acid or alkali. 



World Production 

The countries producing the larger quantities are Canada (chrysotile), the Union 
of South Africa (amosite, blue crocidolite and chrysotile), the U.S.S.R. (chrysotile), 
Southern Rhodesia (chrysotile), United States (mainly chrysotile), Italy (chrysotile 
and tremolite), Swaziland (chrysotile), Cyprus (chrysotile), Australia (crocidolite 
and some chrysotile), France (amphibole), Japan (chrysotile and amphibole) and 
Finland (anthophyllite). The world's recorded production of marketable asbestos 
fibre rose steadily during World War II and immediately afterwards, and in 1957 
totalled about 1,373,000 long tons, excluding outputs from the U.S.S.R., Czecho- 
slovakia, Roumania and North Korea. Of the total production recorded about 
1,250,000 long tons, or 92 per cent., was produced in British countries. About 
90 per cent, of the world's output is chrysotile. 

No marketable asbestos is mined in Great Britain; in 1958 imports of unmanu- 
factured asbestos included 109,765 long tons of crude and fibre, 21,566 long tons of 
waste asbestos and asbestic and 8,595 long tons of asbestos cement products. 
Exports of manufactured asbestos cement products totalled 69,858 long tons. 

Preparation and Grading of Fibres 

The mineral, as obtained from the mines by blasting and quarrying, may be 
dressed and sold either as " crude " or in the form of various grades of fibre which 
have been produced by milling. The content of fibre in the rock mined may range 
between 3 and 10 per cent. 

" Crude " asbestos consists of hand-picked cross-fibre asbestos in its natural 
unfiberized condition, freed from adhering rock by hand cobbing, and small pieces of 
short-fibred material having been rejected. Crude asbestos, as marketed, may still 
contain from 5 to 20 per cent, of rock, dust or short fibre which has to be removed 
by the asbestos spinner in the operation of opening up the fibre. In Canada, crude 
chrysotile is sold in two principal grades, No. 1 being fibre of more than f in. in 
length and No. 2 material varying from | in. to | in. in length. 

The second method of preparing asbestos for the market consists in milling the 
raw material, so as to free the asbestos from the adhering rock and liberate the 
fibres. The problems involved differ from those met with in the usual processes of 
ore dressing or concentration in that the desired mineral and the gangue have the 
same chemical composition and specific gravity, the main difference being that the 
asbestos is fibrous and the process of separation is based on this latter fact. Different 
systems of treatment have therefore to be used to meet the peculiarities of each 

In the case of Canadian chrysotile, the process may be described in general as 
consisting of primary crushing by jaw crushers to about 2 in. in size; drying in 
rotary or stack driers; milling in five or six successive stages of crushing; removing 
sand by screening and lifting the fibre by suction, the final stages of the crushing 
being done by beating machines. Finally, the fibre is graded by sieving on rotary 

Methods for the preparation of amosite or crocidolite from the crude rock differ 



in many respects from those used for chrysotile, owing to the difficulty of separating 
the fibres from a hard gangue. 

There is no generally accepted standard method for grading milled asbestos, 
but the general tendency is now to accept that adopted in Canadian practice 
which is based on a mechanical sieving test using the Quebec Standard 
Testing Machine which consists of a nest of three rectangular wooden sieves 
with a collecting box beneath. The top sieve is J-in. mesh, the second 4-mesh, 
and the third 10-mesh. Sixteen ounces of fibre are placed in the top sieve, 
the lid is closed, and the whole nest shaken for two minutes horizontally 
by a standardized mechanical driver. The contents of each sieve and the box 
are then weighed and the grade of the fibre is determined by the number of ounces 
contained in each. Thus, if 2 oz. remain in the top, 8 oz. in the second, 4 oz. in the 
third sieve and 2 oz. in the box, the fibre is known as 2-8^1—2, one of the spinning 
grades. The complete grading system consists of nine groups, the milled fibres being 
named according to the purposes for which they are mainly employed. The grades 
are shown in Table 19. 

Groups 3, 4 and 5 are each further subdivided into seven sub-grades designated 
by the letters D, F, K, M, R, T and Z, group 6 into one grade only, D, and group 7 
into five sub-grades of fibre testing down to 0-0-0-16, the lowest grades being 
classified by weight per cubic ft. 

Table 19 

Canadian Grades of Crude and Milled Asbestos 

Crude Asbestos 

Group 1 . 
Group 2 

Crude No. 1 . 
Crude No. 2. 
Crude, run-of-mine 
Crude, sundry 

No machine test; crude £ in. and over. 
No machine test; crude | in.-f in. 
Unsorted crudes. 
Crudes other than above. 

Milled Asbestos 

Group 3 . 
Group 4 . 

Group 5 . 

Group 6 . 

Group 7 . 

Group 8 . 

Group 9 . 

Spinning or textile fibre 
Shingle fibre 

Paper fibre . 

Waste, stucco or plaster 

Refuse and shorts 

Sand . 


Testing 0-8-6-2 and over. 

Testing below 0-8-6-2 and including 

Testing below 0-l£-9|-5 and including 

Testing below 0-0-10-6 and including 

Testing below 0-0-5-11 and including 

Mill product weighing over 35 lb. and 

under 75 lb. per cu. ft. Loose measure. 
Mill product weighing 75 lb. per cu. ft. 

and over. Loose measure. 

Standard methods have also been published for the classification of African 
chrysotile, amosite and crocidolite; Russian chrysotile, and Australian chrysotile 
and blue grades. 




The multifarious uses for asbestos may be roughly classified according to the 
type of fibre. Long fibres are used for yarn, cord, braid and textiles; for packing and 
gaskets; for felted long fibre paper, and for filtration and asbestos-cement goods 
where maximum strength is required. Medium length fibres, including short spin- 
ning shingle and paper grades, are used as the reinforcing filler in asbestos cement 
products; as the chief component of asbestos paper and millboard; as the binding 
agent in magnesia insulating compounds; in filtration pads and sheets (felted with 
cellulose), and in moulded brake blocks and linings. Short fibres and floats are used 
as fillers in asphalt, paints and putties, plaster, stucco, plastic mouldings, etc. 

U.S. National Stockpile Specification P-4 R.l. of November 1st, 1954, for the 
purchase of amosite asbestos, requires the material to be equal to that mined in the 
Transvaal, Union of South Africa, and to conform to one of the standard 
commercial grades known as D3 or Dll. Grade DX and Dll amosite, although 
shorter in staple length, shall be equal in quality to that of the longer grade (Grade 
D-3). The amosite shall contain not more than 5 per cent, by weight of foreign 
matter or 2 per cent, of moisture. 

U.S. National Stockpile Specification P-3R.1. of June 6th, 1953, for the purchase 
of non-ferrous chrysotile asbestos suitable for textile products designed for electrical 
insulating applications, requires the product to be equal to or better than that mined 
in Southern Rhodesia at the Shabanie mine. The material should separate easily into 
strong, flexible fibres, that are not harsh or brittle and do not break into shorter 
fibres to an objectionable degree in opening or fiberizing processes. The " soft " 
chrysotile mined in Arizona represents the optimum quality and the " harsh " type 
is not acceptable. 

All chrysotile asbestos shall be commercially non-ferrous and shall conform to 
the following percentage limitations : Total iron by weight, maximum 3 -50 ; magnetic 
iron by weight, maximum 2 00. 

It is also specified that chrysotile asbestos shall conform to one of seven com- 
mercial grades in regard to size, as determined by the Quebec Standard Testing 
machine. The mineral shall contain not more than 5 per cent, by weight of foreign 
matter such as grit, particles of serpentine or other extraneous matter. 

U.S. National Stockpile Specification P-80 R of April 17th, 1952, for the pur- 
chase of crocidolite asbestos provides for three grades of product, which must be a 
blue Bolivian mineral or its equivalent. The asbestos as received must not contain 
over 2 per cent, of moisture or over 5 per cent, of foreign matter (material other than 
fiberizable asbestos), and no animal waste or petroleum products. The three grades 
specified are (a) crude No. 1, which must have at least 85 per cent, (by weight) of 
its fibres f in. or over in length, (6) crude No. 2, in which at least 85 per cent, (by 
weight) shall consist of fibres between f in. and | in. in length, and (c) run-of-mine, 
of which at least 90 per cent, of its lumps and fibres must be retained on a No. 16 
U.S. standard sieve. 

Asbestos-cement Products. These provide the largest outlet for short fibred 
asbestos and constitute the chief demand for the mineral. The asbestos, which is 
generally about $ in. or less in length, acts as a binder for the cement and constitutes 



from 12 to 20 per cent, of the finished articles, which include roofing slates, tiles, 
sheets, gutters, pipes for drainage and many other products. 

The production of asbestos-cement fiat and corrugated sheets and tiles is carried 
out either by dry or wet mixing. In dry mixing the fibre and Portland cement, after 
being well blended in mechanical mixers, is spread evenly on a conveyor belt and 
sprayed with water. It is then compressed by passing between rollers, cut to shape, 
pressed mechanically to remove much of the water and passed to the curing kiln. In 
the wet process, a thin slurry of asbestos and Portland cement is fed into a roll type 
suction calender and the sheet is built up by successive laminations to the required 
thickness. The machines used for making these sheets much resemble those used for 
paper making. 

Over 96 per cent, of the chrysotile asbestos used in the United States in 1958 
was short-fibre material, of less than spinning length, and was mostly used in the 
construction industry. Most of the crocidolite used in the United States was 
employed in asbestos-cement pipe manufacture. 

Asbestos-cement slates have found favour for roofing on account of their light- 
ness compared with natural slates or clay tiles. They can also be produced in a 
variety of colours. Asbestos cement pipes for conveyance of water under pressure 
have been made in this country since 1928, gradually superseding metal or earthen- 
ware pipes for many purposes since they are resistant to corrosion or electrolytic 
action when buried in soil. 

The following figures show the ratio of wet to dry weights of asbestos-cement 
and some other roofing materials: 

l,400^./f. Wet Dry 

Asbestos-cement .... 4 1\ 

Concrete tiles .... 11 10 

Clay tiles .... 11 J 10£ 

Natural slates 5£ 5 

It has been stated that some harsh and semi-harsh chrysotile asbestos fibres 
have some advantages over the softer type for use in certain wet processes for 
making asbestos cement pipes, and it is claimed that any degree of harshness can be 
obtained by a flash-heating process. 

Asbestos Paper and Millboard. These important heat insulating products may 
contain up to 80 per cent, of asbestos compounded with 18-20 per cent, of china 
clay and 2 per cent, of a binder, such as sodium silicate or starch. An important 
development in insulation has been the manufacture of pre-shrunk asbestos paper, 
which does not absorb moisture and so can be used as a pipe covering which will not 
shrink under the influence of heat. The fibres used are generally much shorter than 
those employed for making asbestos-cement products. Asbestos millboard has 
many uses, including the manufacture of gaskets, washers and boarding. Asbestos 
" aircell " insulation for steam pipe covering, and in ovens, is made from thin 
corrugated layers of asbestos sheet cemented to alternate layers of plain sheet. 

Chrysotile asbestos is used in the manufacture of asbestos paper which is 
employed in the electrical industry for insulation purposes. The chief difficulty in its 



production is the elimination of impurities, such as oxides of iron. This has been 
overcome, according to British Patent 512,581, by a method developed by the 
British Electrical and Allied Industries Research Association. Under this patent it 
is claimed that the electrical properties of the asbestos are improved by heating it 
with a liquid containing an aromatic compound having two or more hydroxyl 
groups substituted in the nucleus, e.g. pyrogallol, quinol, resorcinol or pyrocatechol. 

Magnesia-Asbestos Insulation. About 15 per cent, of short-grade spinning fibre 
is incorporated with 85 per cent, of basic magnesium carbonate to produce this 
well-known heat insulating compound, in which the asbestos is employed as a binder. 
The A.S.T.M. standard specification for this product is given under "Magnesium" 
(p. 355). 

Asbestos Filters. The fibres for this purpose are usually J-J in. long, and should 
be well cleaned and freed from dust and impurities. Since amphibole asbestos offers 
much better resistance to attack by acids than does chrysotile, fibres of this type are 
employed in filters. Italian tremolite was formerly used mainly for this purpose on 
account of its resistance to chemicals and freedom from iron, but latterly a type of 
anthophyllite from Maryland, U.S.A., has largely replaced it. 

Jointing. A form of sheeting which can be cut into washers, gaskets or discs, is 
made from a mixture containing from 20-60 per cent, of asbestos with rubber solu- 
tion, fillers and naphtha. The mixture is run through a heated calender and pressed 
into sheet form. A medium length fibre of about J-f in. is used for the better 
quality products, but under i in. in size may be employed in cheaper goods. 

All-Asbestos Heat and Sound Insulators. These are usually composed of either 
blue or amosite asbestos, together with a small amount of a binder; the mass of the 
rough, interlocking fibres binds itself and the resiliency of the fibres makes it possible 
to manufacture a light-weight product. The chief uses for this type of product are for 
the heat insulation of boilers and for bulkhead lining aboard ship to absorb heat 
and noise from the engine rooms. 

A.S.T.M. standard C. 194-48 for Asbestos Thermal Insulating Cement requires 
that the asbestos used shall be Grade 7 or longer, as defined by the Quebec Asbestos 
Producers Association. 

Sound Insulation. For this purpose, fibre of about i in. in length is usually em- 
ployed. The insulation is sometimes attained by pressure spraying a mixture of fine 
fibre (about J in. in length) and an inorganic binder on the surface to be treated. 
After drying, the sprayed surface can be coated with other material, such as stucco. 
This type of sound insulation has been used on the walls of the London Underground 
tubes, and on the bodies, sides and roofs of the trains. 

Asbestos Fabrics. The employment of asbestos for spinning into yarn and cloth 
probably constitutes its second largest use, after asbestos-cement. Both the white 
(chrysotile) and the blue (crocidolite) can be spun into yarn and amosite is also used, 
but only to a limited extent. Only crocidolite, chrysotile and amosite asbestos fibres 
have enough strength and flexibility for processing as textile products. The tensile 
strength of fibres of a particular type naturally varies considerably, but the following 
figures, quoted by C. Z. Carroll-Porczynski, are useful as indicating the range as 
compared with some other fibres: 



Amosite asbestos . 
Chrysotile asbestos 
Crocidolite asbestos 
Tremolite asbestos 
Glass Fibre 
Cotton fibre 

Tensile Strength 

lb./sq. in. 

16,000- 90,000 



1,000- 8,000 


73,000- 89,000 

During the process of opening up, carding and spinning the asbestos fibres are 
subjected to much crushing, bending and flexing, which causes more damage to 
those fibres which are harsh or brittle than to the soft flexible type, and so the 
original length and strength of the fibre may not be a criterion of its suitability for 

A detailed account of the preparation, carding and spinning of asbestos and its 
industrial uses is given in " Asbestos from Rock to Fabric " by C. Z. Carroll- 

Usually the asbestos employed for spinning is of better quality and longer fibre 
than that used in asbestos-cement products. It can be plaited and woven similarly to 
vegetable fibres, and the yarn can be made into tape, cloth, brake-linings, gaskets, 
packings or ropes, which can be reinforced with metal or impregnated with rubber, 
plastics, graphite or other materials. 

White asbestos fabrics are made sometimes from a mixture containing up to 20 
per cent, of cotton, the presence of which enables the shorter fibred grades of asbes- 
tos to be woven. 

Asbestos cloth is valuable on account of its fireproof and heat-resisting qualities 
and finds use in safety curtains for theatres, fireproof gloves and clothing, conveyor 
belts, boiler insulation, and for many other purposes. 

As a general rule, asbestos is unchanged by heating to about 400° C, but above 
this temperature it begins to lose combined water with a decrease in mechanical 
strength. The outer layer of dehydrated fibre may, however, act as a protective 
coating for the film underneath. 

Electrical Insulation. The highest grade of long-fibred white asbestos may be used 
in the production of some types of insulating paper, but it must be free from coarse 
grit, sand, grease and other foreign substances and practically free from iron. 

Large quantities of asbestos are employed to cover electric wire used for traction 
type electric motors and coils where there is a liability of the temperature rising so 
high as to damage the ordinary cotton covering. It is considered by some users that, 
for this purpose, Rhodesian asbestos is superior to Canadian as the latter contains 
ferrous oxide which reduces its insulating properties. 

Asbestos in Thermo-Plastics. Recently new uses have been developed for both 
crocidolite and chrysotile asbestos by employing them, either as loose fibre or in the 
woven form, as matrix materials in certain thermo-setting plastics. 

A wide range of such products is marketed in Great Britain, and examples are 



given below. " Durestos " felt made by Turner Bros. Asbestos Co. Ltd., of Rochdale, 
Lanes., consists of long fibred chrysotile asbestos impregnated with a phenolic resin. 
It is claimed to be particularly suitable for manufacture by low temperature mould- 
ing methods. It is stated to be characterized by its strength, resistance to most acids 
and chemicals, considerable heat and flame resistance and dimensional stability. A 
variety specially resistant to acids is made from crocidolite and a special electrical 
grade consists of long fibred chrysotile in a spirit-soluble cresylic resin. Phenolic- 
resin asbestos laminates in the form of paper are made by Bakelite Ltd. An amphi- 
bole (amosite) asbestos felt for use in making plastics for structural purposes is 
made by the Cape Asbestos Co. Ltd. Asbestos cloth laminates bonded with mela- 
mine resin have found some uses in the electrical industry and silicone asbestos 
laminates for use in the electrical and aircraft industries are made by Midland 
Silicones Ltd. Another asbestos-reinforced silicone product is " Ferobestos " made 
by J. W. Roberts & Co. at Bolton, Lanes. " Marinite," a rigid sheet product con- 
sisting essentially of asbestos and diatomite, is claimed to be useful for heat insulat- 
ing purposes at temperatures up to 900° F. 

An important thermosetting asbestos material for chemical engineering, known 
in the United Kingdom as " Keebush ", and on the Continent and in the U.S.A. 
as "Havag", is a phenol-formaldehyde or cresol-formaldehyde resin filled for 
reinforcement with long asbestos fibres which have been previously digested with 
acid to remove all soluble matter. Keebush is stated to be suitable for tempera- 
tures up to 130°C, resists thermal shock, is a good heat insulator and has good 
wearing properties. 

The various types of moulded goods made include some which, at moderate 
temperatures, are almost unaffected by all but the strongest acids, and others which 
will resist alkalis up to 20 per cent, strength. Other varieties include some very dense 
products suitable for light-weight aircraft bulkhead partitions, which, when sub- 
jected to flame at 1,000°C. only smoulder on the surface, and do not support 

A special type, which contains graphite and asbestos fibre, is claimed to be suit- 
able for bushes and bearings of all descriptions, being hard and unaffected by water 
or lubricating oils. A moulded product, known as phospho-asbestos, is claimed to be 
particularly suitable for contact breakers for electrical purposes. 

Other Uses. Chrysotile asbestos, according to U.S. Patent 2,732,343 of January 
24th, 1956, is an essential component of a new type of drilling fluid, especially 
suitable for use under high temperature conditions. 

Asbestos is employed in some types of smoke filters for cigarettes. 

Asbestos is probably the most extensively used mineral filler in plastics. Its 
principal value is to give resistance to heat. The asbestos used is usually chrysotile in 
the form of " floats," i.e. material varying in size from dust up to -fa-in. fibre. 

Woven tape, which is the basic material for brake linings, may be produced 
from both metallic and non-metallic asbestos tape impregnated with a plastic and 
cured under pressure. 




" Chrysotile Asbestos, Its Occurrence, Exploitation, Milling and Uses." By F. Cirkel. Canad. 

Dept. Mines, Rep. No. 69, 2nd Ed., 1910, 316 pp. 
" Blue Asbestos — Bibliography on Acid Resisting." Science Library Bibliog. Ser. No. 112, 1933, 

" Asbestos in the Manufacture of Rubber Products." By M. E. Lerner. Asbestos, 1934 (Nov.), 

" Asbestos: Domestic and Foreign Deposits." By O. Bowles. U.S. Bur. Mines Inform. Circ. No. 

6790, 1934, 24 pp. 
" Uses for Blue Crocidolite Asbestos." By L. W. Dennis and A. W. Koehler. Asbestos, 1935 

(May), 2-6. 
" Asbestos Cement Products." Asbestos, 1936 (Aug.), 2-16. 
" Asbestos, with Special Reference to its Manufacture (exclusive of Patents). Science Library 

Bibliog. Ser. No. 282, 1936 (60 references). 
" Asbestos." By G. E. Howling. Min. Res. of the Br. Empire and Foreign Countries. Imperial 

Institute, Lond., 2nd Ed., 1937, 88pp., including bibliography. 
" The Manufacture of Asbestos Products." By R. S. Gardner. Bull. Canad. Inst. Min. Met., 1942, 

45 (No. 366), 488-496. 
" The Grading of Asbestos." Anon. Canarf. Min. J., 1944, 65, 604-605. 
" Processing of Asbestos Fibres." 'By M. S. Badollet. Canad. Min. Metall. Bull., 1950, 53, 

" Asbestos, A Mineral of Unparallelled Properties." By M. S. Badollet. Canad. Min. Metall. 

Bull., 1951,54, 151-160. . „ „• . T r ^ a a 

" Plastics Containing Asbestos as a Reinforcing Filler." By P. H. H. Bishop, J. E. Gordon and 

P. L. McMullen. Plastics Progress, British Plastics Convention, 1953. 
" Handbook of Asbestos Textiles." Textile Inst., Philadelphia, 1953, 78 pp. 
" Asbestos, Its Origin, Production and Utilization." By W. E. Sinclair. Lond., 1955, 365 pp. 
" The Asbestos Industry." By O. Bowles. U.S. Bur. Mines Bull, 552, 1955, 122 pp. 
" Heat Treatment of Chrysotile Asbestos Fibres." By M. S. Badollet and W. C. Streib. Canad. 

Min. Met. Bull., 1955, 48, 65-69. , ,„„,„„„ 

" Asbestos from Rock to Fabric." By C. Z. Carroll-Porczynski. Manchester, 1956, 400 pp. 
" Asbestos." By G. F. Jenkins. " Industrial Minerals and Rocks." Amer. Inst. Min. Met. and 

Petrol. Eng., 3rd Ed., 1960, pp. 23-53. 
" Asbestos. A Materials Survey." By O. Bowles. U.S. Bur. Mines Inf. Circ, 7,880, 1959, 94 pp. 
" Asbestos." By D. O. Kennedy. " Mineral Facts and Problems." U.S. Bur. Mines Bull. 585 

1960 (preprint), 8 pp. 
" Asbestos." Minerals Yearbook, U.S. Bur. Mines (Annual). 

Standard Specifications 

American Society for Testing Materials 
A.S.T.M. Standards, 1958. 

Asbestos Thermal Insulating Cement, C. 194-48. 
U.S. National Stockpile Specifications: 

Amosite Asbestos. P-4-RI, November 1st, 1954. 

Chrysotile Asbestos. P-3-RI, June 10th, 1953. 

Crocidolite Asbestos. P-80-R, April 17th, 1952. 

Asphalt and Bitumen 

A large variety of bituminous substances are used in industry, some being natural 
asphalts whilst others are end-products from the processing of bitumens, petroleum, 
or vegetable substances. This latter group, which includes residues from the distilla- 
tion of oils derived from coal, lignite, shale, wood, rosin, etc., is too large to be 
considered here, but readers wishing to pursue this branch of the subject will find 
much information in the volumes on " Asphalt," by H. Abraham, which deal very 
thoroughly with uses and sources of supply. In this volume, therefore, it is proposed 
to consider only native asphalts and asphaltites. 



Some differences in the terminology of asphalt occur between current practice 
in the United States and in Europe, particularly in relation to road paving and 
surfacing materials. 

In the United States the term " asphalt " is reserved by the trade for solid or 
semi-solid products in which the principal constituents are bitumens. In Europe, 
however, mineral matter is deemed to be an essential constituent of asphalt, which 
includes bituminous rock but not semi-solid or solid petroleum residua which are 
termed bitumen. Thus, the British Standard Specification No. 596 for Mastic 
Asphalt Surfacing defines natural asphalt rock as " a naturally occurring consoli- 
dated rock impregnated with bitumen exclusively by a natural process; the term to 
exclude artificial mixtures of non-bituminous limestones with bitumen of any 
source and description." 

The classification of native asphalts and bitumens, in relation to one another 
is somewhat difficult on account of their wide variety, but possibly that proposed 
by H. Abraham, and summarized below, will best serve our purpose. 

Classification of Native Bitumens 

1 . Petroleums — solids or viscous liquids. 

2. Native asphalts — solid or semi-solid; 

A. Pure or nearly pure, such as Bermudez Lake asphalt from Venezuela. 

B. Associated with mineral matter: 

(1) Trinidad Lake asphalt; 

(2) Iraq, Boeton, and Albania (Selenitza) asphalts; 

(3) Rock asphalts, e.g. Val de Travers. 

3. Asphaltites — hard. 

A. Pure or nearly pure : 

(1) Gilsonite; 

(2) Grahamite or raphaelite; 

(3) Glance pitch — Manjak. 

In assessing the value of asphalt or bitumen it is customary to take into con- 
sideration a large number of physical, and some chemical, properties. These often 
include specific gravity, hardness, softening and flowing temperatures, penetration 
at several temperatures, ductility, solubility in some organic solvents such as carbon 
disulphide, carbon tetrachloride or 88° naphtha, and the percentages of carbenes, 
asphaltenes, mineral matter and water. It is evident, of course, that although such 
constants are recorded in the larger text books, space is not available here to quote 
more than a few figures under the different headings. 

Sources of Supply 

Petroleum Bitumen. Asphaltic bitumens may be obtained from asphaltic, semi- 
asphaltic or non-asphaltic petroleum and are of three main types: (1) residual 
asphaltic bitumen produced by distillation from natural petroleum, (2) blown 
asphaltic bitumen produced from residual oils by blowing with air at temperatures 
between 350 and 525°F., (3) pressure-still asphaltic bitumen obtained from the 



residuum from cracking crude petroleum. All these materials are available with a 
wide diversity of properties and, being of the nature of by-products from the 
petroleum industry are not dealt with in this volume. 

Native Asphalts — Solid and Semi-solid. So far as is known deposits of pure or 
nearly pure native asphalt are no longer worked on a large commercial scale. At 
one time fair quantities of a material containing about 95 per cent, of bitumen were 
produced by treating an asphalt mined at Bermudez Lake in North Eastern 
Venezuela, but no output has been recorded since about 1933. It was principally 
used for making emulsified asphalt for road surfacing and for roofing. 

Asphalts Associated with Mineral Matter. Trinidad Lake asphalt is obtained 
from deposits at La Brea, where the asphalt covers an area of about 100 acres and 
has a depth at the centre of 285 ft. The product excavated is essentially an emulsion 
of water and bitumen which carries in suspension a considerable quantity of 
extremely finely divided clay, much of which seems to have colloidal properties. 
A recorded analysis of the crude asphalt shows the following composition: 

Per cent. 

Water and gas volatilized at 100°C. . . . 29-00 

Soluble in carbon disulphide .... 39-30 

Mineral matter (on ignition) .... 27-20 

Water of hydration and adsorbed bitumen . . 4-50 


The asphalt is refined, before shipment, by heating it by steam in large open vats, 
a treatment which removes much of the water, causes the heavier mineral matter to 
sink, and allows the refined product to be strained into barrels for shipment. 

Refined Trinidad asphalt has a softening point of 183-189°F. (R. & B. method), 
a specific gravity of about 1 -4, and carries about 36 per cent, of mineral matter. 
The bituminous constituents are all entirely soluble in carbon tetrachloride and 
about 85 per cent, are soluble in 86° naphtha. 

As Trinidad Lake asphalt is too hard for many industrial uses, it is often softened 
by admixture with light petroleum residuum or natural petroleum, the resultant 
product being termed " asphalt cement "; it can be readily blended with coal tar, 
vegetable and mineral oils, waxes and pitches, and is extensively used in street 
paving, the manufacture of asphalt roofing and shingles, mastic asphalt, coatings 
for iron pipes, etc. 

In addition to the outstanding deposits in Trinidad several similar, but smaller, 
deposits are worked elsewhere. A fairly hard asphalt containing about 10-20 per 
cent, mineral matter is mined in Albania and marketed under the name of " Selen- 
itza." The material has been used locally, after softening with petroleum products, 
for paving, mastic and bituminous coatings. 

A deposit occurring on the island of Boeton (N.E.I.) contains bitumen associated 
with microscopic coral shells and clay, and is used locally for paving. 

Asphalt, associated with about 25 per cent, of mineral matter and 10 per cent, 
of insoluble organic matter, occurs in Iraq near Baghdad and is used locally, after 
mixing with an aggregate, as a paving material. 

Rock Asphalt. This mineral substance usually consists of a calcareous rock, such 



as limestone, naturally impregnated with bitumen. Deposits of such material occur, 
and have been worked, in Europe in the Val de Travers region of Switzerland, near 
Ragusa in Sicily, and various localities in France and Germany. Most of the 
European deposits yield a product which carries from 6-11 per cent, of bitumen. 
Rock asphalt is used principally for paving and road making purposes, for lining 
water tanks and reservoirs, and for flooring, and as an ingredient in mastic asphalt. 

The largest deposit in the United States occurs in Kentucky and contains from 
3 to 12 per cent, of soft asphalt, which is mixed with sand. The material is sold 
locally under the name of " Kyrock." Other deposits of bitumenous limestone or 
sandstone occur in Texas, Oklahoma, Louisiana, Alabama and Utah. 

Asphaltites are naturally occurring substances which are characterized by having 
fusing points usually above 230°F. They are often divided into three groups 
termed respectively gilsonite, glance pitch, and grahamite but, as all are probably 
derived from the metamorphosis of petroleum, the three types often tend to merge. 

A scheme designed to differentiate between the three types, based upon their 
physical properties when relatively free from mineral matter, proposed by H. 
Abraham, is shown in Table 20. 

Table 20 



Sp. gr. at 77° F. 

Softening point 

(K. & S. 

method) ° F. 

Fixed carbon 
Per cent. 

Gilsonite . 

Glance pitch or manjak 

Grahamite . 


103-1 10 

1 15-1 -20 



Gilsonite and glance pitch mix in all proportions with fatty acid pitches and so 
differ from grahamite. 

Gilsonite is found in quantity only in one region in Utah, U.S.A., where it 
occurs as nearly vertical veins up to 22 ft. in thickness. Reserves are estimated at 
25 million tons. Gilsonite is a black mineral having a conchoidal fracture, brown 
streak and a hardness of about 2. Usually about 98 per cent, is soluble in carbon 
disulphide but the solubility in petroleum naphtha varies from 10-60 per cent. The 
quantity of mineral matter is usually less than 1 per cent. 

Gilsonite is generally marketed in two grades termed respectively " Selects," 
" V.B." and " Sparkling black." " Selects " are material having the lowest softening 
point, taken from the centre of the vein and show the characteristic lustre and 
conchoidal fracture. They have a greater solubility in petroleum naphtha than the 
less fusible grades. When treated with a petroleum solvent the " Selects " do not 
" liver " or gel whereas the other grades may do so. 

The softening point in the best grade, known as " selects," ranges from 270 to 
300°F. (R. & B. method), while that in the less fusible grades, such as those 
designated as " V.B." and " Sparkling black," may range up to about 380°F. 



The behaviour in petroleum solvent is determined by dissolving 30 parts of 
gilsonite in 70 parts of petroleum naphtha (by weight) under a reflux and, after 
allowing to cool, observing whether a permanent liquid solution is obtained or one 
which gels immediately or on standing. 

Gilsonite is miscible in all proportions with drying oils and with the resins 
commonly used in making varnishes. It also blends with petroleum residuum and 
other asphalts and when compounded with them is widely used in making black 
varnishes and baking japans. 

On account of its high dielectric strength it is widely used in the manufacture of 
cases for electrical storage batteries, thermo-plastic moulded goods and in battery 
sealing compounds. It also finds use in mastic floorings, brake linings and impreg- 
nated fabrics, pipeline coatings and, when dissolved in turpentine or xylol, as a 
pigment in some printing inks. 

The American Gilsonite Co. of Salt Lake City, Utah, have recently introduced 
a product which they term " Gilsulate," a blended mixture of crushed gilsonites 
which can be used for insulating underground metallic pipelines against corrosion. 
It is used by applying the powder to the pipe, tamping down and then heating the 
pipe so as to cause the gilsonite to melt and give complete protection. 

The American Gilsonite Company's plant converts part of the mineral mined 
at their holding in E. Utah into high grade coke, with high-octane gasoline 
as an important by-product, the output of the latter being about 1,300 barrels 

Grahamite resembles gilsonite in appearance but has a higher specific gravity and 
melting point, and is more friable. It occurs in Mexico, Argentina, Trinidad, 
Oklahoma (U.S.A.), and Cuba. Grahamite differs from gilsonite and glance pitch 
in that on heating it does not melt readily, but intumesces. 

No extensive use has been made of grahamite, but, formerly, the mineral from 
Oklahoma, U.S.A., was used for blending with petroleum residuum to give a 
product of a rubbery consistency which was used for coating paper and in roofing 
felt. Although grahamite does not melt when heated alone it can be fluxed with 
certain types of petroleum residuum at about 500° F. to produce the above-mentioned 
rubber-like product. 

Glance Pitch. This mineral, which is also known as manjak, occurs in Cuba, 
Columbia, Utah (U.S.A.), Mexico, the U.S.S.R., and the Island of Barbados. It is 
roughly intermediate in physical properties between gilsonite and grahamite, being 
more difficult to fuse and less soluble in petroleum naphtha. It has been used to 
some extent as a substitute for gilsonite in making varnishes and in thermo-plastic 

Pyrobitumens. Wurtzilite, or Elaterite, is an asphaltic pyrobitumen noted for its 
hardness and infusibility. It is a brittle mineral, having a bright lustre and a mineral 
content usually under 5 per cent. It is mined to a small extent in Vintah County, 
Utah, U.S.A. After being cracked and depolymerized, it gives a product sometimes 
used in paints or varnishes. 

Ozokerite is a solid bitumen found in Galicia, Roumania, the U.S.S.R., and 
Utah, U.S.A. It is used in high-grade candles, rubber goods and floor polishes. 



World Production 

The world's production of natural asphalt in recent years is shown in Table 21, 
which is necessarily incomplete owing to the fact that official statistics of production 
of natural asphalt are published by only a few countries. 

Table 21 

Production of Natural Asphalt* 


Long tons 






Albaniat • 
United States 

(sales) Gilsonite 
Argentina Gra- 

hamite (export) 























* From Statistical Summary of the Mineral Industry, 1953-8, Mineral Resources 
Division, Overseas Geological Surveys, London, 1960. 

t In 1953 Albania produced 50,000 long tons of natural asphalt. 
% Information not available. 

The world's production of asphalt rock in recent years as far as statistics are 
available is shown in Table 22. 

Table 22 
Production of Asphalt Rock* 

Long tons 












Federal Germany 


















Belgian Congo . 





— • 

United States 




















* From Statistical Summary of the Mineral Industry, 1953-8, Mineral Resources 
Division, Overseas Geological Surveys, London, 1960. 
t Information not available. 


In many industrial processes it is frequently not a single asphalt which is used, 
but rather a combination of bituminous substances, some of which may be by- 



products added for fluxing purposes. One example of this is the fluxing of Trinidad 
asphalt with a by-product from the distillation of crude petroleum. 

Indications have already been given of the uses for which particular types are 
suitable and it will only be necessary here to deal in general terms. 

Electrical Uses. On account of their high breakdown voltage, and resistance to 
moisture, acids, alkalis, changes of temperature, and weathering, high grade asphalts 
are particularly useful in many electrical insulating compounds. In these cases the 
asphalts may be mixed with resins, rubber, wood tar pitch, montan wax, etc. 

The principal use, nowadays, is for such purposes as filling electrical junction 
boxes and in mixtures used for making battery containers. 

A variety of bituminous compositions are used for the former purpose, one 
mixture including refined asphalt, 75 per cent.; elastic pitch, 10 per cent.; rosin oil, 
5 per cent. The refined asphalt used has a melting point of 340° F., ash 01 per cent, 
and a specific gravity of about 1 -02. 

With regard to the use of refined asphalt in mixtures for making battery con- 
tainers, one authority claims that it should not contain excessive percentages of iron 
or manganese compounds as these are injurious to the performance of the battery. 
Some bituminous paints are used as insulating varnishes. 

Japans and Asphaltic Paints. The term " japan " should correctly be reserved for 
a protective coating which has been hardened by baking. Such coatings may be 
made from the best quality gilsonite, petroleum asphalt or coal tar pitch. Gilsonite 
gives hard films of good appearance, which have good elasticity and a coefficient of 
expansion close to that of iron, a property which makes them of value as a protective 
coating for that metal. 

For a general-purpose Brunswick black paint, a cheaper material than the 
relatively expensive gilsonite may be employed, provided that the contents of 
mineral matter and of free carbon are not too high in the material selected for use. 
Such paints may consist of an asphaltic or bituminous base, a drying oil, a resin and 
some stearin pitch. 

In black lacquers of the nitrocellulose or cellulose ester type, it is usual to 
employ a high grade asphaltite. 

Bituminous emulsion paints are finding an extended use for such purposes as 
coating damp walls or on fresh concrete. , 

Asphaltic Roadways and Pavements. Asphaltic and bituminous products are used 
extensively in highway construction work, both as foundation and surfacing materi- 
als. Asphaltic products are valued for this work principally on account of their 
binding and waterproofing properties, resistance to weather, and their ability to 
give a certain amount of flexibility to the road surface. 

The materials used vary considerably in their composition and physical proper- 
ties and range from Val de Travers bituminous limestone up to high grade asphalts 
and bituminous emulsions. Residuals from petroleum refining are largely employed 
for direct use, for fluxing natural asphalts, and for making bituminous emulsions. 

The asphaltic mixtures used for constructional work may be roughly grouped 
into: (1) rolled asphalt, (2) mastic asphalt, and (3) compressed rock asphalt. 
Rolled asphalt is the name given to asphalt mixtures which are consolidated with 



the aid of a roller. It is only used for paving. Mastic asphalt is a mixture of a graded 
aggregate and a bituminous binder in such proportions as to yield a plastic and 
voidless mass, which when applied hot can be trowelled to any form or contour. It 
differs from rolled asphalt in having a higher bitumen content and a higher per- 
centage of small particles in the aggregate. Compressed rock asphalt is a natural 
limestone rock impregnated with bitumen, ground to a fine powder, enriched if 
necessary with extra bitumen, and is spread on the road in the form of a hot powder. 

The properties required in asphaltic substances vary according to the mode of 
use, which may range from coating broken stone for foundation mixtures up to the 
rich fine-grained mixtures or bituminous emulsions for surface treatment. 

A large number of official specifications dealing with asphalt and bitumen, for 
various specific purposes, have been formulated by the British Standards Institution, 
the American Society for Testing Materials and numerous Federal State bodies in 
the United States and elsewhere. These specifications are too numerous to be dealt 
with here, but some of the more important are listed under " Specifications " 


" Bibliographies of the Modern Asphalt Industry." Science Library Bibliogr. Ser. No. 130, 1934 

(18 references). 
" The Science of Petroleum," Ed. by A. E. Dunstan, A. W. Nash, E. T. Brooker and H. Tizard. 

Lond., 1938. Vol. 4: " Bituminous Paints," by L. A. Jordan, pp. 2747-59; " Native Asphalts 

and Bitumens." By J. S. Miller, pp. 2710-27. 
" Typical Asphalt Specifications for Road and Pavement Construction." By J. S. Miller. " Science 

of Petroleum," 1938, pp. 2742-46. 
" Electrical Bitumens. Properties and Applications." By E. E. Halls. Industr. Chem., 1942, 18, 

51-54, 76-78. 
" Asphalts and Allied Substances." By H. Abraham. 4th Ed. (2 vols.), New York, 1945, 2142 pp. 
" Bituminous Coatings for the Protection of Iron and Steel." By R. St. J. Preston. D.S.I.R. Chem. 

Res. Special Rep. No. 5, 1947, 39 pp., including bibliography. 
" The Waterproofing of Fibrous Materials, with Special Reference to Wax and Bitumen Treat- 
ment of Papers and Cordage." By E. E. Halls. Industr. Chem., 1948, 24, 37-45. 
" A Study of Asphalts and Asphaltic Materials." By G. W. le Maire. Colorado Sch. Mines 

Quart., 1953, 48, No. 2, 87 pp. 
" Current Practice in Asphalt Manufacture." Indust. Chem., 1955, 31, 252-3. 
" Gilsonite as a Source of Synthetic Fuel." By P. L. Cottingham et al, Industr. Engng. Chem., 

1955, 47, No. 2, 328-332. 
" Hot Asphalt Construction." By P. C. Leaver. /. Inst. Petrol, 1957, Sept., 247-271. 
" New Jet Mining Method Stopes Gilsonite for Gasoline." By G. O. Argall. Min. World (San 

Francisco), 1957, 19, No. 10, 68-71. 
" Mining Gilsonite by Hydraulic Methods." Min. Jour. (Lond.), 1960, 254, 94-95. 

Standard Specifications 

American Society for Testing Materials 
A.S.T.M. Standards, 1958: 

Emulsified Asphalt, D 977-49. 

Asphalt Mastic for Use in Waterproofing, D 491-41. 

Asphalt Cement for Use in Pavement Construction, D 946-47T. 
British Standards Institution: 

Rolled Asphalt, Asphaltic Bitumen and Fluxed Lake Asphalt. Hot Process. B.S. 594 : 1958. 

Mastic Asphalt (Natural Rock Asphalt) Aggregate for Roads and Footways. B.S. 1446 : 1948. 

Mastic Asphalt (Limestone Aggregate) for Roads and Footways. B.S. 1447 : 1948. 

Compressed Natural Rock Asphalt. B.S. 348 : 1948. 

Bitumen Macadam with Igneous Rock. B.S. 1621 : 1954. 

Fine Cold Asphalt. B.S. 1690 : 1950. 

Bitumen Macadam with Gravel Aggregate. B.S. 2040 : 1953. 

Mastic Asphalt for Roofing. B.S. 988 : 1957. 

Mastic Asphalt for Flooring. B.S. 1076 : 1956. 

Mastic Asphalt for Damp-proof Courses. B.S. 1097 : 1958. 



Mastic Asphalt for Roofing (Natural Rock Asphalt). B.S. 1162 : 1957. 

Pitch Mastic Flooring (with Trinidad Lake Asphalt). B.S. 1177 : 1944. 

Asphalt Tiles for Paving and Flooring (Natural Asphalt Rock). B.S. 1324 : 1946. 

Coloured Pitch Mastic Flooring (incorporating Trinidad Lake Asphalt), B.S. 1783 : 1951. 


The only barium minerals used commercially are barytes and witherite, most of the 
world's demand being met by supplies of the first named. 

Barytes, which consists essentially of barium sulphate, has a specific gravity 
ranging between 4-25 and 4-5, a hardness varying between 2-5 and 3 -5, but generally 
about 3, and a refractive index of 1 -636. British barytes frequently contains small 
quantities of strontium sulphate (0-2-1-6 per cent.) and calcium sulphate (up to 
0-7 per cent.) in solid solution. 

Barytes is frequently found associated with other minerals, but its high specific 
gravity often enables it to be separated from them by means of log washers or other 
similar appliances. Since 1941, flotation processes have been increasingly employed 
in the United States for producing high grade barytes concentrates. 

The mineral, as found, may vary in colour from white to pinkish, and may be 
stained by iron oxide or carbonaceous matter. It occurs in both " hard " and 
" soft " forms, the latter being preferred and sometimes specified, when the material 
has to be finely ground, such as when required for use in paint. Hard barytes can be 
used for the manufacture of barium chemicals or lithopone. 

Table 23 

Analyses of Some British Barytes. 
Per cent. 





Barium sulphate, BaS0 4 





Strontia, SrO . 





Silica, Si0 2 





Iron oxide, Fe 2 O a 





Alumina, A1 2 3 





Lime, CaO 





Magnesia, MgO 



— ■ 


Carbon dioxide, CO a 





Fluorine, F. 





Manganese, Mn 





Copper, Cu 





Zinc, Zn 





Lead sulphide, PbS 





Soda, Na 2 




(1) Force Crag, Cumberland. 
(3) Malehurst. 

(2) Silverband mine, Westmorland. 

(4) Grade A. T., Long Fell, Westmorland. 



For the production of the best grades of white barytes, it is frequently necessary 
to submit the ground mineral to a bleaching process, such as bleaching with 
hydrochloric or sulphuric acid, washing and drying. Occasionally, barytes occurs 
contaminated with small amounts of bituminous matter and, although this renders 
it unsuitable as a white filler, it does not usually prevent its use for chemical purposes. 

As a general rule, barytes mines submit the crude mineral to various dressing 
processes designed to separate as high a percentage as possible of first-grade white 
barytes and most mines market several grades of product. Hence it is difficult to 
quote analyses which would be representative of the output from any particular 
region. The analyses in Table 23, however, show the chemical composition of some 
good quality British barytes as marketed by the producers (see p. 59). 

World Production 

The world's recorded production of barytes rose steadily from about 1-64 
million long tons in 1951 to about 2-83 million long tons in 1957, and then dropped 
to about 2-2 million long tons in 1958. The chief producing countries in order of 
importance are: The United States, Federal Germany, Mexico, Canada, Greece, 
United Kingdom, Yugoslavia, Peru, and France. No figures are available for the 
production of China, Czechoslovakia, Norway and the U.S.S.R. 

During World War II the production of barytes increased considerably in some 
countries. Thus Canada, whose production amounted to only a few hundred tons in 
1940, reached a peak production in 1956 of 286,460 long tons. 

In Great Britain the total production in 1958 of barytes and witherite amounted 
to 59,052 long tons, of which 13,442 long tons was marketed ground but not 
bleached. The production of witherite has not been separately recorded since 1947, 
when it amounted to 14,727 long tons. Great Britain's imports in 1958 consisted of 
32,111 long tons of unground barytes and 17,822 long tons of ground barytes, in 
addition to 2,507 long tons of manufactured barium compounds (excluding blanc 
fixe). Canada produced about 10,600 lb. of metallic barium in 1948, but in 1949 
the output was only 2,116 lb. The United States produces several thousand pounds 
of barium metal annually. 


Barytes in its natural condition, after suitable grinding, is used principally as a 
pigment or extender in paints; in the heavy muds used in oil-well drilling; as an 
inert filler in the manufacture of oilcloth, linoleum, paper and plastics; and as a 
weighting material for textiles and leather. It is also used to a small extent as a 
flux in brass melting, when it is said to act mainly as a scavenger. 

Chemical industry uses barytes chiefly for the manufacture of barium compounds 
such as the chloride, nitrate, carbonate, hydrate, and sulphide; the latter for making 
the white pigment lithopone. At one time, barium peroxide, made from barytes, was 
used in the manufacture of hydrogen peroxide, but this method has now been largely 
replaced by an electrolytic process which uses alkali persulphates. 

The relative amounts of barytes used for the several purposes indicated above 
naturally vary with the country concerned and official figures are rarely available, 



except for the United States, where the official consumption by uses is divided into 
two categories (a) crude, and (b) crushed and ground barytes. In 1958 the total 
consumption of crude barytes was 1-2 million short tons, of which amount 88 1 
per cent, was used for the production of ground barytes, 11-4 per cent, in the 
manufacture of lithopone and 8-9 per cent, for making barium chemicals. Of the 
ground barytes marketed in 1958, about 95 per cent, was used in oil-well drilling, 
1 per cent, in glass manufacture, 1 per cent, as a paint filler and 2 per cent, in rubber 

The annual consumption of barytes for the more important uses in Great 
Britain is approximately as follows: lithopone, 65,000 tons; barium salts, 15,000 
tons; paint 40,000 tons; and coal washing, 6,000 tons. 

Paint Manufacture. For use as a pigment or extender, the barytes should nor- 
mally be as white as possible. The colour of stained barytes can sometimes be 
improved by bleaching with dilute hydrochloric or sulphuric acid, a treatment which 
is usually effective if the staining is on the surface, or confined to cleavage planes, 
but is often unsuccessful with minutely crystalline barytes. This treatment, however, 
is not usually effective in removing staining due to manganese oxides, and in such 
cases the mineral may be roasted with nitre and salt, and leached with sulphuric acid, 
thus removing both manganese and iron oxides. Some off-colour barytes is, however, 
used as an extender in dark paints. 

Some paint manufacturers operate their own deposits, whilst others purchase the 
mineral finely ground and ready for incorporation in paint. 

Most standard specifications for barytes for use as a pigment or extender deal 
with the ground product as offered to the trade. 

British Standard Specification B.S. 1795 : 1952 provides for two grades of 
natural barytes (which may have been bleached) for use as extenders in paints as 



Total residue on Sieve 

volatile at 
98°-102° C. 


in water 


Acidity or 




Grade 1 . 
Grade 2 . 

Per cent. 


Per cent. 

Per cent. 

Per cent. 

Per cent. 

Per cent. 

* Calculated as H 2 S0 4 or Na a CO a . 

The normal range of oil absorption for barytes is between 6 and 12 for Grade 1, 
and between 8 and 14 for Grade 2. 

One important user in Great Britain specifies that deliveries of " best barytes " 
shall conform to the following specification: BaS04, not less than 98 per cent.; 
volatile matter at 95-98°C, 0-5 per cent, maximum; carbonates, expressed as 
CaC03, 0-5 per cent, maximum; matter soluble in water, 1 per cent, maximum. 
The water-soluble extract must be neutral to methyl red. As regards freedom from 
gritty and abrasive particles, deliveries must conform to a sample provided by the 



buyer and the whole must pass a 240-mesh British Standard sieve. The oil absorption 
of the material, determined by a prescribed method, must not be less than 9 or 
greater than 14. 

Specification S.A.B.S. 41 1-1952 issued by the South African Bureau of Standards 
requires barytes for use as an extender for paints to conform to the following per- 
centage chemical composition: barium sulphate (min.), 92-0; matter soluble in 
hydrochloric acid, 1-5 (max.); matter soluble in water, 0-5 (max.); moisture and 
volatile matter, 0-5 (max.); alkalinity, calculated as Na2C03, 01 (max.) acidity, 
calculated as H 2 S0 4 , 0-1 (max.). As regards fineness, all the barytes should pass 
a 200-mesh A.S.T.M. sieve and not more than 0-5 per cent, be retained on a 
325-mesh sieve. Its oil absorption should be not less than 10 or more than 14. 

British Standard Specification 1795 : 1952, for blanc fixe as an extender for 
paints, requires that it shall contain not less than 95 per cent, barium sulphate; 
not more than 02 per cent, shall be retained on a 100-mesh sieve and not more 
than 0-15 per cent, shall be retained on a 240-mesh sieve; matter volatile at 
98-102°C. shall not exceed 05 per cent; matter soluble in water shall not exceed 
0-5 per cent, excluding alkaline earth sulphates; and the acidity or alkalinity shall 
not exceed 1 per cent. 

The standard specification of the American Society for Testing Materials 
No. D 602-42, for barytes for use in pigments, requires a minimum of 94 per cent. 
BaS04, with the following maxima for other ingredients : ferric oxide, 05 per cent. ; 
water-soluble matter, 0-2 per cent.; moisture and volatile matter, 0-5 per cent.; 
quartz, clay or other foreign substances, 2 per cent. Coarse particles retained on a 
325-mesh sieve (44 microns) must not exceed 0-5 per cent. 

The A.S.T.M. specification for blanc-fixe (precipitated barium sulphate) for 
use as a pigment is the same as for barytes, except that it requires a minimum of 
97 per cent, of BaSC>4 and the maximum for ferric oxide is 02 per cent. 

For the preparation of barium sulphide for the eventual production of lithopone, 
some British users specify a barytes containing 95 per cent, or over of BaS04, a 
maximum limit of 1 per cent, of iron oxide, and relative freedom from mud, clay, 
and any siliceous minerals which may flux at temperatures below 1,300°C, the 
furnace temperature usually employed for reducing barytes to the sulphide with coal 
or coke. The efficiency of reduction may be seriously impaired by the presence of 
some compounds of iron or manganese; galena (lead sulphide) does not appear to be 
harmful up to about 3 per cent., unless iron compounds are also present. Fluorspar 
is objectionable as it causes attack on the furnace linings. Iron oxide, alumina or 
silica are undesirable as they may react with the barytes to give compounds which 
are insoluble in water. It is stated that 1 per cent, of iron oxide may render 4 per 
cent, of barium sulphide inactive. Over 5 per cent, of silica is often considered 
objectionable, as it tends to flux and form barium silicate, which may occlude 
barytes. Silicates are, on the whole, less deleterious than free silica (quartz). Ease of 
crushing, high porosity and absence of any serious amount of decrepitation on 
heating are also of importance. As barytes for the above use is generally required to 
pass a i-in. screen, jig concentrates are quite suitable. 

Chemical Industry. In barytes for chemical purposes, such as the manufacture 



of barium compounds, colour is not important, chemical composition and physical 
condition being the determining factors. In general, it may be said that the chemical 
composition of barytes sold in Great Britain for chemical manufacture varies 
between the following percentage limits; BaSO-i, 90-98; Si02, 0-5-3-5; Fe203, 
trace to 2; AI2O3, trace to 1. Small amounts of Ca, Mg, Mn, Pb, Zn, Cu and F may 
also be present. 

The usual method for obtaining soluble barium compounds from barytes is by 
roasting the coarsely ground mineral, mixed with carbon, in a rotary kiln at 
about 1,300°C. By this means the insoluble barium sulphate is reduced to the 
sulphide which can be leached with water to give the so-called " black-ash " solution 
which contains Ba(OH>2 and BaSH 2 . This solution, when reacted with zinc sulphate 
gives a precipitate of barium sulphate and zinc sulphide, which constitutes the white 
pigment, lithopone. When commercially pure " blanc fixe " is required, the black 
ash solution is precipitated with sodium sulphate. 

If the black ash solution is precipitated with sodium carbonate, the insoluble 
barium carbonate obtained can be used to prepare barium oxide, hydroxide, 
peroxide or nitrate. 

Barium peroxide is made by heating the carbonate, at about 1,200-1,250° C, in 
a tunnel furnace with carbon, usually pitch. By this means is produced barium 
monoxide, BaO, which can be converted to the peroxide, Ba02, by heating it in a 
stream of dry air at about 600° C. 

A German Specification in use before 1939 for chemical barytes required the 
mineral to carry 93-96 per cent. BaS04 with not over 4 per cent. Si02, nor over 3 
per cent. Fea03. 

About 80 per cent, of the lithopone produced is used in paint, about 10 per cent, 
in floor coverings and textiles and 1 per cent, in rubber. 

Ceramic Uses. Barytes has been suggested as a main constituent in mixtures for 
whiteware, which are claimed to mature at lower temperatures, but show maturing 
ranges 3-11 times greater than those of the conventional semi-vitreous body- 
mixtures. Barytes is sometimes used in certain ceramic glazes and for this purpose 
should not contain more than 05 per cent, of iron oxide. 

Glass Manufacture. Some specifications require 96 per cent, or over of BaS04 
with not more than 0-1 per cent. Fe203, any iron introduced from the crushing 
plant being removed magnetically. Size and grading are important, the material 
often being required to pass a 16-mesh screen with not more than 5 per cent, passing 
100-mesh, but on the other hand, some users employ a more finely ground product 
and allow up to 40 per cent, of the material to pass a 100-mesh sieve. 

Another specification requires not less than 96 per cent. BaS04; moisture, 
maximum 3 per cent.; Fe203, maximum 0-4 per cent.; Ti02, trace; the product 
ground to pass 16-mesh with not more than 3 per cent, over 20-mesh and not more 
than 40 per cent, passing 100-mesh. Barytes is useful in batch mixtures for making 
glass in continuous tanks as it dissolves in the soda ash to form a heavy solution 
which sinks to the bottom of the tank, and when the temperature is raised it reacts 
with silica to give gaseous sulphur dioxide and oxygen, which tend to stir the melt 
and remove occluded gases. 



Oil Well Drilling. Finely ground barytes mixed with colloidal clay is used in the 
heavy liquids (" muds ") employed in oil well drilling in order to hold back the gas 
until the well casing is in position. In the United States, where in 1958, 95 per cent, 
of the output of ground barytes was so used, one large user specifies barytes 
having a specific gravity of at least 4-2 and a content of barium sulphate over 89 per 
cent. Other users require a minimum of 93 per cent. BaS04, with water soluble 
matter not exceeding 0-1 per cent. Certain users specify that not more than 5 per 
cent, of the barytes shall be retained on a 325-mesh sieve. Some barytes may show 
poor wetability by water or clay suspensions and hence is not particularly suitable 
for this use. The consumption of ground barytes for this purpose averages about 1 
ton per 100 ft. of well drilled. 

Paper Industry. Ground barytes is used as a filler in the manufacture of Bristol 
board and similar heavy stiff products, also where a brilliant white finish is required, 
as for playing cards. For these purposes a good white high quality product is required. 
Precipitated barium sulphate is used in the manufacture of photographic paper. 

Rubber Manufacture. This usually calls for a product containing over 99-5 per 
cent. BaS04, with only traces of silica, iron oxide, alumina and manganese, and 
hence the material mostly used is chemically prepared blancfixe, as natural barytes, 
even of the highest grade, rarely approaches this standard of purity. Some bleached 
natural barytes is, however, used in the United States for this purpose. 

Coal-washing. A suspension of finely ground barytes and clay is used in the 
Barvois system of coal-washing. Much of the barytes is recovered for re-use, but 
there is a loss of about 3 lb. or less per ton of coal cleaned. 

Electronics. In recent years considerable use has been made of barium titanate in 
electronics. One method of producing the compound in the form of single crystals is 
by fusing a mixture of barium titanate, ferric oxide and potassium fluoride and 
cooling the melt at a controlled rate so as to obtain crystals in the form of thin 
plates which are annealed by slow cooling. Barium titanate has a crystalline struc- 
ture similar to that of the mineral perovskite. The compound may be employed 
either in the form of single crystals or in a polycrystalline form in a ceramic mixture. 
Barium titanate ceramics which have been permanently polarized exhibit piezoelectric 
properties similar to those of the single crystal material. Such ceramics have un- 
usual electro-mechanical properties, which make them valuable for use in trans- 
ducers, gramophone pickups, thickness gauges, accelerometers and digital com- 
puters. A useful account of the piezoelectric and other uses for barium titanate 
products is given in the pamphlet issued by Technical Ceramics Ltd., of Towcester, 

The barium titanate complex for use in electronics may vary considerably and 
occasionally substantial quantities of magnesium or strontium are incorporated to 
give a material having special properties for electrical purposes. One such product 
made by the National Lead Company of the U.S.A. has the basic composition 
shown in Table 24. 

Metallurgy. Metallic barium, which is available in commercial quantities, is 
usually made by the guntz process by reducing barium oxide, BaO, by means of 
metallic aluminium or silicon at about 1,200°C. in an electric furnace, under a 



Table 24 

Barium Titanate: National Lead Co., U.S.A. 

Per cent. 

Titanium dioxide, TiOa 34-3 

Barium oxide, BaO . . . . . .63-9 

Strontium oxide, SrO . . . • • .03 
Magnesia, MgO . . . . . . .0-2 

Lime,CaO 01 

Alumina, AI2O3 0-8 

Silica, Si0 2 0-5 

Zirconia, ZrOz 005 

reduced pressure of about 0-5 mm. At the temperature of the operation, the metal 
is vaporized and collected in a special condensing chamber. 

Metallic barium, which has a white colour is an extremely active deoxidizer, 
readily burns to the oxide, and combines with many gases and is therefore of service 
as a " getter " for removing traces of gases from radio valves. Some of the physical 
properties of pure metallic barium are as follows : 

Atomic number . 

Atomic weight 

Melting point 

Boiling point 

Crystal structure 

Thermal neutron cross-section absorption 

Isotopes (stable) . 

Density (at 20°C.) 

Specific heat (at 20°C.) 





Body-centred cubic 

1 -3 barns 

Ba-130, 132, 134, 135, 136, 137, 138 


068 cal./g./°C. 

Metallic barium produced by Dominion Magnesium Ltd. of Toronto, Canada, 
has the following average percentage composition: barium, 98; strontium, 1; 
calcium, 0-4; magnesium, 0-4. 

A range of barium-aluminium and barium-magnesium alloys, known as " Baral " 
and " Barmag " respectively, containing from 25-50 per cent, of barium, are made 
in Great Britain for this purpose. 

Lead-calcium-barium alloys, containing about 2 per cent, of barium, known as 
Frary metal, are self hardening and have been used for bearings. Such alloys can be 
produced by the electrolysis of a mixture of the molten chlorides. During World 
War II, lead alloys containing barium as a hardening agent were used for bearings, 
one such alloy containing: barium, 0-4 per cent.; calcium, 0-7 per cent.; sodium, 
0-2 per cent. ; and 04 per cent, of either lithium or magnesium. 

Other Uses. Barytes has been used as an aggregate in heavy concrete for shields 
from radiation at atomic energy plant. Barytes behaves like an ordinary aggregate 
and concrete can be obtained having a density up to 232 lb. per cu. ft. For details 
regarding this use the articles by L. P. Witte and J. E. Backstrom (1954) and by 
H. S. Davis (1958) should be consulted. 

Barium phenolate is used as the starting point in the manufacture of certain 

M.C.A.I.— D 



plasticizers and barium radio-isotopes are used in tracing the flow of fluids through 
pipes. Porous barium oxide (BaO), produced by the well regulated reduction of pure 
barium carbonate by means of carbon, is used for drying or dehydrating certain 
gases, liquids and solids at temperatures up to 1,000°C. The compound is very 
porous, reacts violently with water and dissolves in methyl alcohol to give barium 
methylate, which is useful for methylating reactions. 

A mixture of unvulcanized rubber and barytes has been used with an asphalt 
spread in a number of streets in Rapid City, South Dakota, the mixture being termed 
" Rubarite." 


Natural barium carbonate, witherite, is a white mineral having a specific gravity 
of about 4-3 and a hardness of 3 to 3 -75. 

It is not a rare mineral, but deposits capable of yielding economic quantities are 
rare, in fact, so far as is known the only ones which have been operated in recent 
years are the Holmside mine, Co. Durham (from 1932 to 1958) and the Settlingstone 
mines, near Hexham, Northumberland, which have been producing regularly since 
1872 and now have an output of about 10,000 tons per annum. The owners of 
Settlingstone Mines Ltd. market the following three main grades of witherite: 

(a) Smalls containing about 90 per cent, of BaCo 3 ; size | in. to fines. 

W >> » " '* >» » » » » » 

(c) Fines „ „ 85 „ „ „ . 

Pulverized witherite is also marketed in the following sizes: 81-82 per cent, 
through 300-mesh and 92 per cent, through 200-mesh (93-95 per cent. BaC0 3 ), and 
air floated: 99-5 per cent, through 300-mesh (93-95 per cent. BaC0 3 ). 

Table 25 shows analyses of two lump grades (1) and (2) as produced at the 
Holmside mine and (3) the 90 per cent, grade from Settlingstones. 

Table 25 

Grades of British Witherite. 
Per cent. 




Barium carbonate, BaCO s 




Calcium carbonate, CaC0 3 




Magnesium carbonate, MgCO a 




Barium sulphate, BaS0 4 . 




Ferric oxide, Fej0 3 . 




Alumina, Al a 3 




Silica, SiO a 




Carbonaceous matter 




Zinc sulphide, ZnS . 










Chemical Industry. When available, witherite is often preferred to barytes as 
the starting point for the manufacture of barium chemicals such as the nitrate and 
chloride, on account of its ready solubility in nitric or hydrochloric acid. 

Some makers of barium nitrate prefer pea-size mineral containing at least 90 
per cent, barium carbonate, with as little iron oxide as possible, but no specific 
maximum is laid down for this latter constituent. 

The colour of the mineral is little criterion of its suitability, as all shades of grey 
are used, but over 10 per cent, of impurity is undesirable owing to difficulties en- 
tailed in the filtration of the barium nitrate solution. As a general rule iron- 
containing minerals are not objectionable unless the iron can be readily dissolved in 
nitric acid or is very finely divided. 

Paint Manufacture. During World War II the possibility of using ground 
witherite as an extender received consideration. The function of witherite as an 
extender in paints is claimed to be its colour stabilizing effect on acid-sensitive 
coloured pigments which enhances the durability of exterior paints. 

British Standard Specification B.S. 1795 : 1952 for Extenders for Paints requires 
natural witherite to contain not less than 93 per cent, of barium carbonate. The total 
residue on a 100-mesh B.S. sieve must not exceed 01 per cent, and that on a 240- 
mesh sieve is limited to 0-6 per cent. Matter soluble in water must not exceed 0-5 per 
cent, and the acidity or alkalinity of the sample must not exceed 015 per cent, 
calculated as H2SO4 or Na2CC>3. The maximum for matter volatile at 98-102°C. 
is -5 per cent. The normal range of oil absorption of natural witherite for use as an 
extender in paints is usually between 8 and 12. 

British Standard Specification 1795 : 1952, for precipitated barium carbonate for 
use as an extender for paints, requires that it shall have a minimum content of 98 
per cent, barium carbonate; matter retained on a 100-mesh sieve, not exceeding 
0-25 per cent.; matter retained on a 240-mesh sieve, not exceeding 0-5 per cent.; 
matter volatile at 98 to 102°C, not exceeding 0-5 per cent. ; matter soluble in water, 
not exceeding 0-75 per cent. The alkalinity or acidity of the aqueous extract shall 
not exceed 0-5 per cent. The material shall not yield more than 0-3 per cent, of 
matter insoluble in hydrochloric acid when examined by the prescribed method. 
The material shall not contain more than 01 per cent, of oxidizable sulphur 
compounds, expressed as hydrogen sulphide (HaS) when tested by the prescribed 

Brick Making. Natural witherite finds a use as a preventative against " scum- 
ming " which is liable to appear on fired bricks when the clay used contains sul- 
phates of calcium, magnesium or the alkali metals. Its function is to convert the 
relatively soluble sulphates to the much less soluble barium sulphate (solubility 1 in 
400,000). The best results are said to be obtained with air-floated witherite, the 
consumption averaging about 8 lb. of the mineral per ton of clay treated. 

Case-Hardening. Witherite has been used to some extent, mixed with wood 
charcoal, for case-hardening certain steels. The useful component in the mineral 
appears to be the carbon dioxide which is evolved on heating and is reduced by the 
hot carbon monoxide to carbon which in turn reacts with the steel to produce a 

s 2 



hard wearing high carbon surface. The barium oxide remaining after the reaction 
can be regenerated to carbonate by exposure to the air or carbon dioxide. 

Ceramic Uses. Witherite is finding increasing use in Great Britain in the ceramic 
industry. The mineral has been found to be quite suitable for replacing precipitated 
barium carbonate in the manufacture of barium-flint glasses, a specially high grade 
pulverized material being sold for this purpose. Ground witherite is also being used 
in the manufacture of frits and enamels. 

Other Uses. Some witherite has been used for the treatment of industrial 
effluents from chrome plating and anodic oxidation processes in order to remove 
small traces of chromic and sulphuric acids which are toxic to the organisms necessary 
for sewage purification. Witherite is also claimed to be an effective rat poison when 
mixed with a suitable bait. 


" Sur la Preparation du Bariums pour a partir de son sous oxide." By A. Guntz. Comp. rend. 

" Witherite: Its Occurrence and Uses." By H. C. Meyer. Foote Prints, 1932, 5 (No. 1), 3-19. 
" Processing Witherite." By H. C. Meyer. Engng. Min. J., 1933, 134, 283-84 
" Some Notes on Drilling Muds." By P. Meyer. /. Inst. Petroleum, 1934, 20, 10-33. 
" Barytes and Witherite." By J. Simpson. Min. Industr. of the Br. Empire and Foreign Countries, 

Imperial Institute, Lond., 2nd Ed., 1937. 84 pp., including bibliography. 
" Barium and Strontium Nitrates in Safety and Distress Signals." By H. C. Clauser. Foote-Prints. 

1937, 10 (No. 1), 21-28. 
" Witherite in Case Hardening." By J. M. Noy and L. G. Bliss. Foote-Prints, 1939, 12 (No. 2), 

15-26, including bibliography. 
" Witherite as a Preventative of Fluorescence [in brickmaking.] " Anon. Br. Clayworker, 1940. 

49, 127-28. 
" Marketing of Barite." By B. L. Johnson. U.S. Bur. Mines, Inform. Circ. No. 7149, 1941, 16 pp. 
" Barytes at Pembroke, Hants. Co., Nova Scotia." By C. O. Campbell. T. Canad. Inst. Min. Met.. 

1942, 45, 299-310. 
" Witherite." By F. W. Muddiman. /. Oil Col. Chem. Assoc, 1942, 25, 127. 
" Barytes and Barium Pigments." By J. J. Bradley, Jr. " Protective and Decorative Coatings." 

Ed. by J. J. Mattiello. Lond., 1942, Vol. 2, pp. 428-36. 
" Processes for Making Barium and Its Alloys." By W. J. Kroll. U.S. Bur. Mines, Inform. Circ. 

No. 7327, 1945, 16 pp., including bibliography. 
" Barium Chloride from Witherite; Holmside and South Moor Collieries Process." Anon. 

Industr. Chem., 1946 (July), 22, 393^100. 
" British Barium Products in the Paint Industry." By M. Schofield. Paint Manuf., 1946, 16. 

" Outlines of Paint Technology." By N. Heaton. 3rd Ed., Lond., 1947, 448 pp. (Barium Pigments, 

pp. 91-8.) 
" Drilling Mud." By J. Wojcik. /. Inst. Petroleum, 1948, 34, 291a-92a. 
" Barium Minerals." By F. J. Williams. " Industrial Minerals and Rocks." Amer. Inst. Min. Met. 

Eng., 2nd Ed., 1949, pp. 77-94. 
" Properties of Heavy Concrete made with Barite Aggregate." By L. P. Witte and J. E. Back- 

strom. Proc. Amer. Concrete Inst., 1954, 26 (Sept.), 65-88. 
" The Production of Reproducible Barium Titanate." By R. M. Callahan and J. F. Murray. Bull. 

Amer. Ceram. Soc, 1954, 33 (May), 131-133. 
" Method of Growing Barium Titanate Single Crystals." By J. P. Remeika. /. Amer. Chem. Soc. 

1954, 76, 940-1. 

" Barium Titanate and Other Ferro-Electrics." By M. McQuarrie. Bull. Amer. Ceram. Soc. 

1955, 34, 169-172, 256-266, 295. 

" Modified Barium Titanates." By W. W. Coffeen. /. Amer. Ceram. Soc, 1956, 39, 154, 
"Modified Barium Titanates." Plessey Co. Ltd. U.S. No. 2,742,370, 1956. 
" Barite in Ceramic Whiteware." By R. Ralston Jr., C. Valencia and H. W. Emrich. J. Amer. 

Ceram. Soc, 1956, 39 (No. 2), 73-82 
" High Density Concrete for Shielding Atomic Energy Plants." By H. S. Davis. Proc. Amer 

Concrete Inst., 1958, 54, 965-977. 
" Barium Minerals." By D. A. Probst. " Industrial Minerals and Rocks." Amer. Inst. Min. Met. 

Petrol. Eng., 3rd Ed., 1960, 55-63. 
" Barium." By A. Maillard, Nouveau Traite de Chimie Minerale, Ed. by P. Pascal. Paris, 1958 

Vol. IV, pp. 746-927. 



"T.C.L. Piezoelectric Ceramics." (Barium Titanate.) Technical Ceramics Ltd., Towcester, 

Northants. 1959, 17 pp. 
" Barite." U.S. Bur. Mines, Minerals Yearbook. (Annual). 

Standard Specifications 

American Society for Testing Materials 
A.S.T.M. Standards, 1958: 

Barium Sulphate Pigments. D 602-42. 

Zinc Sulphide Pigments. D 477-45. 
British Standards Institution: 

Extenders for Paints. B.S. 1795 : 1952. 

Lithopone for Use in Paint. B.S. 296 : 1952. 


The name bentonite is applied to a variety of naturally occurring clay-like products, 
which are characterized chiefly by the property of adsorbing water to a greater extent 
than ordinary plastic clays, and by a much greater capacity for base exchange than 
that possessed by kaolinic clays. In certain bentonites the adsorption of water is 
accompanied by a considerable increase in volume and the formation of a gelatinous 

Bentonites are also distinguished from ordinary clays by the fact that they con- 
sist almost entirely of the crystalline clay-like minerals comprising the montmoril- 
lonite family which, in general, may be represented by the formula (Mg.Ca)0. 
Al203.5Si0 2 kH 2 0, where n is equal to about 8. Bentonite has been defined as a 
transported stratified clay which has been formed by the alteration of volcanic 

Bentonite is known and marketed under various synonyms such as soap-clay, 
mineral soap, wilkinite, staylite, vol-clay, aquagel, ardmorite, reunite; most of these 
being trade names for prepared bentonites. 

Properties of Bentonites 

Practically all natural bentonites contain small fragments of other minerals, 
termed " grit," such as felspar, calcium carbonate, gypsum, quartz, etc. This grit 
may constitute from 5-10 per cent, of prepared commercial bentonites. Certain 
gritless bentonites, termed " dust " grades, produced by air-flotation are, however, 
marketed for use where freedom from grit is essential. 

Bentonites range in colour, when dry, from cream to olive green; in specific 
gravity from 2-4-2-8, and in refractive index from 1-547-1-557. Fusion points 
range from about 1,330 to 1,430°C. 

For commercial purposes, bentonites may be roughly divided into two groups, 
(a) those which adsorb a large percentage of water with the accompaniment of 
considerable swelling, and remain in suspension for long periods in water dis- 
persions; (b) bentonites which do not swell to any appreciable extent when wetted, 



and do not remain suspended in thin water dispersions. Between these two groups, 
bentonites intermediate in properties occur. 

Swelling, or colloidal bentonite, is characterized by the fact that it may adsorb up 
to 5 times its weight of water and increase in volume up to 15 times its dry bulk. 
When treated with 18-20 parts of water, such bentonite will form a thin sol in which 
the mineral will remain suspended almost indefinitely. The swelling property is 
reversible, as the material can be dried and re-swelled an infinite number of times 
and still retain its properties. Many sodium bentonites are unaffected by temperatures 
up to 205° C. and so can be dried and wetted any number of times without losing 
their properties. 

When dispersed in water, bentonites rapidly break down into very small particles. 
Thus, the prepared varieties of Wyoming bentonite when so treated yield about 
60-65 per cent, of particles finer than 0-1 micron whilst about 90 per cent, are finer 
than 0-5 micron and about 97 per cent, will pass a 325-mesh (44 micron) sieve. 
Non-swelling, or calcium bentonites, also break up to small-sized particles, usually 
rather coarser than those yielded by the swelling bentonites. 

The chemical composition of some commercial bentonites is shown in Table 26, 
which illustrates the differences in regard to content of alkalis and calcium, between 
the highly colloidal, or sodium bentonites, from Wyoming and other varieties. 

Table 26 

Chemical Composition of Commercial Bentonites. 
Per cent. 


Panther Creek 


" Volclay " 



Silica, SiO a 




Alumina, A1 2 3 . 




Ferric oxide, Fe 2 3 

3 03 

} 4-70 { 


Ferrous oxide, FeO 


Titanium dioxide, Ti0 2 


Lime, CaO 




Magnesia, MgO . 




Potash, K 2 



\ 109 

Soda, Na a O 



Phosphoric anhydride, P 2 O s 




Sulphuric anhydride, S0 3 


. — 


Other minor constituents 



Combined water . 


8 00 


Another useful property of the sodium bentonites is that of base exchange. Thus, 
in water suspension, sodium bentonites will give up sodium and potassium in 
exchange for calcium or magnesium and will also react strongly with salts of some 
organic bases which they can extract from solutions. 

This base exchange property is well illustrated by the figures shown in Table 27, 
which have been published for certain United States bentonites, the values being 
expressed in milli-equivalents per 100 gm. of clay, Kentucky ball-clay being 
included for comparison. 



Table 27 

Exhangeable Metallic Bases in Bentonites 

Sodium bentonite 

Calcium bentonite 

Ball clay 

Calcium, Ca . 
Sodium, Na . 
Potassium, K . 
Magnesium, Mg 












* Corrected for sulphates. 

World Supply 

The world's chief supply of bentonite is obtained from the United States, whose 
output in 1958 was 1,153,048 long tons. 

The mineral is found in nearly every State west of the Mississippi River, and 
also in a belt extending from Kentucky to the Gulf. Over one-half of the output 
comes from the Wyoming-South Dakota area, which yields the sodium, or high- 
swelling, type. Another producer is Panther Creek, Mississippi, which yields the 
non-swelling, or calcium, type. Western Canada has numerous deposits of bentonite, 
the chief being in Southern Manitoba, which yields a calcium bentonite claimed to be 
valuable for oil-bleaching purposes (either in its natural state or after activation), or 
for foundry use. An activating plant is in operation in Winnipeg. Smaller quantities 
are also produced in Alberta, which yields the swelling type. 

In the past up to 70,000 tons per annum of calcium bentonite have been pro- 
duced in Germany, mostly from the Munich area. 

One of the largest known deposits of bentonite outside the United States, is that 
occurring on the Isle of Ponza, one of the Pontine Islands of Italy. This bentonite is 
characterized by its extremely low content of iron oxide. Both sodium and calcium 
bentonites occur in, and have been exported from, French Morocco and Algeria. 
Bentonites have also been produced in Australia, New Zealand, Japan and the 

Statistics of world production are rather incomplete, but available figures for 
lecent years are shown in Table 28 {see p. 72). 

Mining and Preparation 

In most cases, the deposits now being worked for bentonite occur within a few 
feet of the surface and are worked opencast. Workable seams in the Wyoming- 
South Dakota region of the United States vary in thickness from 1-3 ft. and average 
about 30 in. The amount of overburden to be removed varies up to 25 ft., but 
probably averages about 15 ft. 

High colloidal swelling bentonites, as mined, usually contain up to 30, or even 
45, per cent, of water and so the first treatment is drying, usually in rotary kilns 
heated by oil or natural gas. The dried bentonite is next ground, often in bowl-type 
roller mills so as to yield a 200-mesh powder. For certain purposes granular products 



Table 28 

World Production of Bentonite* 

Long Tons 

Producing Countries 








Cyprus (e) . 














Australia (b) . . 







New Zealand 















Greece . 





















Morocco (North) 





\ 4,897 


Morocco (South) 





United States (c) 










15,000 (d) 

20,000 (rf) 







■ — 


Bentonite is also produced in Canada, Germany, Yugoslavia, Algeria and Japan. 

* Statistics supplied by the Statistical Section, Mineral Resources Division, Overseas 
Geological Surveys, London. 

(a) Not available. 

(b) Including bentonitic clay. 

(c) Sold or used by producers. 

(d) Estimated. 

(e) Exports of bentonitic clay. 

are required, hence some of the dried bentonite is sold unground in the form of 
particles, mainly between J in. and 20-mesh size. 

Activation of Bentonites. Many bentonites may be activated by suitable acid and 
heat treatment and so rendered more suitable for use in the clarification of oils. The 
exact mode of treatment varies somewhat with the particular bentonite to be acti- 
vated, but the two following processes may be described as typical. 

In one case, the sun-dried mineral is crushed to 100-mesh and heated with a 
25 per cent, solution of sulphuric acid. The treated earth is then washed, dried and 
crushed to pass 200-mesh. This treatment removes some of the alumina and all the 
combined water and so destroys the colloidal condition of the bentonite. 

In another process, the clay is dried at about 110°C, finely ground and then 
digested with 96 per cent, sulphuric acid for several hours. The treated clay is then 
washed and dried. 

A process, used at one time in Germany for activating some non-swelling 
bentonites, consisted in mixing the dry mineral with soda ash so as to produce a 
swelling variety which was marketed as " Tixoton." Another German activated 
bentonite is " Tonsil." 


The percentage of the total consumption of bentonite in the United States for 
various purposes in recent years is shown in Table 29. 



Table 29 

Consumption of Bentonite in the U.S.A. 


Percentage of Total 







Rotary drilling mud 

Filtration and decolourization of oils . 

Foundry sand bond 

Miscellaneous* ..... 









The consumption of bentonite in the United States in 1958 totalled 1,246,824 long tons. 
* Including use in lightweight aggregates. 

Minor uses include its employment as an emulsifying agent for asphaltic and 
resinous substances; in soaps, paints, and pharmaceutical products; as an adhesive 
agent in horticultural sprays and insecticides; in concrete mixtures, and as a plasti- 
cizer in ceramic bodies. 

In the United Kingdom there are no generally accepted specifications for benton- 
ite, but in the United States specific methods of evaluating bentonite for two of the 
most important uses (in moulding sands and in oil-well drilling) have been laid 
down. Otherwise, no extensively developed, or generally accepted, specifications are 
in use. 

Refining Oils and Fats. Considerable quantities of bentonite are used in refining 
petroleum products and vegetable oils, and in the treatment of fats and greases. 

In treating petroleum both the swelling and non-swelling types are employed, the 
latter, often after activation, to remove tarry complexes and dissolved colouring 
matter, the last-named by selective adsorption. The quantity required depends 
upon the nature of the products treated and varies from about 1 lb. per barrel of 
petrol, up to about 100 lb. per barrel of dark, heavy, lubricating oil. In some cases 
the bentonite can be rejuvenated for further use. 

Drilling Muds. Bentonite is valuable as a constituent of drilling muds owing to its 
thickening and suspending properties and its ability to act as a thin seal. Bentonite 
used for this purpose is generally of the sodium or swelling type and of lower grade 
than that used for oil refining. A number of tests have been formulated by the 
American Petroleum Institute to assist in the selection and evaluation of suitable 

Foundry Uses. The third largest use for bentonite is in foundry practice, where the 
mineral is employed as a bonding agent and conditioner in moulding sand used for 
casting ferrous and non-ferrous metals. In fact, it has been claimed that its use for 
this purpose is standard practice in most Canadian and United States foundries. 
Bentonite is stated to be particularly useful as a bond with the high silica sands used 
in steel foundries and as an ingredient in core washes, in which it serves to keep the 
carbonaceous ingredients in suspension. 

Bentonite used as a bonding agent may be either the sodium swelling type or a 
calcium bentonite, according to requirements. The selection of a suitable bentonite 



is a matter which has received much attention, particularly in the United States. 
The cementing or bonding power, the amount of moisture necessary to develop 
maximum green strength, the high dry-bond strength, the effect on the permeability 
of the mould, the refractoriness, the life during repeated use, are all important 
considerations. The American Foundrymen's Association has laid down methods 
by which these factors shall be determined for a given bentonite. 

Bentonites for incorporation in foundry sands are usually sold in powder form, 
90-95 per cent, of which will pass a 200-mesh sieve. 

Detergents. Bentonite of the swelling type is a constituent of many proprietary 
detergents sold in Great Britain, the United States and Germany for scouring 

One user in Great Britain requires a white or nearly white product which will 
form a viscous solution with ten times its weight of water. The product must be of 
such fineness that 98 per cent, will pass a 120-mesh sieve, and 90 per cent, a 240- 
mesh sieve, whilst the residue must not contain grit or hard particles. The loss on 
drying at 100°C. is limited to 15 per cent, the pH of a 25 per cent, suspension in 
distilled water must not be less than 8 or more than 9 when determined by the glass 
electrode. The bentonite must also have a packing density of not less than 0-85, and 
2 gm. of the mineral must swell to 10 ml. when treated with water in accordance with 
the specification requirements. 

Bentonite is also used in certain soaps to the extent of about 25 per cent. 

Ceramics. Small quantities of bentonite are sometimes incorporated in white- 
ware ceramic bodies to increase plasticity and modulus of rupture, both before and 
after firing, and also as a suspending agent in glaze mixtures. Colour is of minor 
importance, but a maximum swelling capacity is most desirable. A qualitative test 
sometimes applied to bentonite for these uses is to mix the mineral with 5 per cent, 
of MgO, agitate the mixture with 25 times its weight of distilled water and allow it to 
stand for twenty-four hours. Under these conditions the best grade bentonites will 
form a stiff jelly which will have a pH value of about 11-5. 

Many bentonites contain too much iron for use in ceramics, an exception, 
however, being the mineral produced from Ponza, one of the Italian Pontine Islands, 
which has large deposits yielding material carrying less than 1 per cent, of iron oxide. 

Horticultural Uses. Bentonite is sometimes used in emulsion sprays for horticul- 
tural purposes and as a carrier or diluent for poisons, such as nicotine sulphate, 
pyrethrum and rotenone. Colloidal mixtures of bentonite and sulphur are employed, 
under various trade names, as fungicides and animal dips. Dust spray mixtures of 
similar composition are largely used in some areas of the United States for scattering 
by aeroplane. 

Other Uses. Minor uses for bentonite include the employment of an alkali 
bentonite, mixed with glycerine, in some facial beauty creams, in the de-inking of 
old newsprint, as a thixotropic agent to prevent settling of mixed paints, in bleach- 
ing crude sulphur and as an addition to Portland cements and pozzolanas, to in- 
crease their workability and decrease their permeability by solutions. The use of 
bentonite in certain electrical insulating compositions is dealt with in U.S. patent 
2,739,085 of 1956. 



Some of the swelling types of bentonites have been successfully used for making 
earthen dams and reservoirs more resistant to percolating water. The method is to 
mix the soil with 5-10 per cent, of dry bentonite and apply a layer of the mixture, 
several inches thick, to the surface of the walls and bottom of the reservoir. 

Calcium, or non-swelling bentonites, are sometimes used for clarifying used 
solvents which have been employed in dry cleaning. 

A very extensive survey of the occurrence, properties and uses of bentonite, and 
a useful bibliography of the patent literature, is given in Technical Paper No. 609 
issued by the United States Bureau of Mines in 1940. 


" The Properties of Some Clay-like Materials of the Bentonite Type." By H. G. Schurecht and 

H. W. Douda. J. Amer. Ceram. Soc., 1923, 6, 940-8. 
" Possible Industrial Applications of Bentonite." By H. S. Spence and M. Light. Canad. Dept. 

Mines, Bull. 723, 1931, pp. 12-34, including bibliography and patents reference list. 
" Bentonite Technology and Industrial Uses." Amer. Colloid Co., 1935 et seq. (series of industrial 

" Testing and Grading Foundry Sands and Clays. Standards and Tentative Standards." American 

Foundrymen's Association, 4th Ed., 1938, 61 pp. 
" Bleaching Clays Find Increasing Use." By G. A. Schroter. Engng. Min. J., 1939, 140, 35-38 and 

" Bentonite: Its Properties, Mining, Preparation and Utilization." By C. W. Davis and H. C. 

Vacher. U.S. Bur. Mines, Tech. Paper No. 609, 1940. 83 pp., including bibliography and list 

of U.S. Patents classified according to uses. 
" Laboratory Methods for Evaluating the Physical Properties of Bentonite." Amer. Colloid Co. 

Data No. 251, 1945, 4 pp. 
" Fineness as a Factor in Bentonite Usage." Amer. Colloid Co. Data No. 203, 1945, 4 pp. 
" Bentonite and Fuller's Earth." By N. H. Fisher. Miner. Res. Australia, Sum. Rep. No. 30, 

Canberra, 1946, 21 pp. 
" Properties and Testing of Bentonite." By D. G. Beech and M. Francis. Trans. Ceram. Soc, 

1946, 45, 148-60. 
" Bentonite." [Description and foundry uses.] By L. Sanderson. Mine & Quarry Engng., 1948, 14, 

" Bentonite." By G. L. Gillson. " Industrial Minerals and Rocks," Amer. Inst. Min. Met. Petrol. 

Eng., 3rd Ed., 1960, pp. 87-91. 
" La Bentonite, les Argiles Colloidales et leurs Emploi." By M. Deribere and A. Esme. 3rd Ed., 

1951, Paris, 224 pp. 
" Clays." U.S. Bur. Mines, Minerals Yearbook. (Annual). 


" Recommended Practice on Standard Field Procedure for Testing Drilling Fluids." Amer. 
Petrol Inst., Code 29, 1st Ed., 1938, 6 pp. 


The only commercial ore of beryllium of any importance is beryl, a silicate of beryl- 
lium and aluminium (3BeO.Al203.6SiC>2). Commercial samples of the mineral 
usually carry from 10-5 to 12 per cent, of beryllium oxide (BeO) as compared with 
14 per cent, required by the above formula. Accessory constituents in the ore may be 
alkalis, iron oxide, lime, magnesia, phosphorus and sulphur. 

The chemical composition of a good quality commercial beryl is as follows: 



BeO, 11-8; A1 2 3) 22-5; FeO, 0-4; CaO, 1-4; MgO, 0-3; K 2 0, 0-2; Na 2 0, 11; 
Si0 2 , 62; P, Oil, and S, 02 per cent. 

Commercial beryl is usually yellowish or greenish white in colour, has a specific 
gravity of about 2-7, a hardness of about 7| and a refractive index of 1 -584. The gem 
variety, emerald, is transparent and grass green in colour, whilst aquamarine is 
usually pale greenish blue. 

Beryl is rarely found in sufficient quantities to make it worth while working an 
occurrence solely for the mineral. 

World Production 

In recent years the world's supply of commercial beryl, as shown by official 
statistics, has been obtained chiefly from Brazil, Belgian Congo, Argentina, Moz- 
ambique, Southern Rhodesia, India, United States, South West Africa, Australia, 
the Union of South Africa, Madagascar and Portugal. Statistics of production, 
imports and exports of beryl are very incomplete, as evidenced by the fact that 
imports into the United States alone for 1956 nearly equalled the world's recorded 
production. The country importing the largest quantities of beryl is the United 
States, which has taken steadily increasing amounts in recent years and reached a 
peak of 11,046 long tons in 1956, but fell to 4,106 long tons in 1958. Exports of 
beryl from the principal producing countries to the United Kingdom totalled 
255 long tons in 1958. 

In view of its importance in connection with atomic research problems, some 
countries have placed restrictions on the export of beryl and beryllium ores. These 
include India, Madagascar, the Union of South Africa and South- West Africa. 

The export of beryl and other beryllium ore from the Union of South Africa and 
South- West Africa has been prohibited since 1948, except under permit issued by the 
Chairman or Deputy Chairman of the Atomic Energy Board. 

Extraction from Ores 

The processing of beryl for the production of its compounds and alloys is carried 
out principally in the United States (where three refineries are in operation), in 
France, and in the United Kingdom. 

Preparation of Beryllium from Beryl. Beryl ore is very resistant to attack by 
chemical means, in fact at normal temperatures hydrofluoric acid is practically the 
only reagent which attacks the mineral to any extent. For this reason all processes 
for the extraction of beryllium start with the treatment of the ore at high 

The two processes now in general commercial use are: (1) a fusion process and 
(2) mixing with an alkali metal double fluoride and roasting at a controlled 

In the Brush Beryllium Company's hydroxide process the beryl is rendered 
reactive by crystallographic changes in the ore molecule induced by heat. The ore is 
melted in a carbon lined 3-phase electric furnace and is then poured through a high 
velocity jet into a water quenching tank. The quenched frit is screened to remove 
larger pieces which are returned for further treatment. The frit obtained is ground 



to pass 200-mesh and mixed with a calculated quantity of concentrated sulphuric 
acid. The acid slurry is pumped in a small jet on to the preheated (25O-30O°C.) 
sulphating container, which is an autogenous lined gas-fired steel mill. After sulphat- 
ing, the mixture is leached with water, the silica remaining insoluble. Two general 
methods have been proposed for separating beryllium from the sulphate solution :(1 ) 
fractional crystallization, (2) fractional precipitation. The crystallization method 
depends upon the addition of ammonia to the solution and the subsequent removal 
of most of the aluminium as ammonium alum, the remainder being eliminated at a 
later stage as sodium aluminate. The sodium beryllate solution is treated to pre- 
cipitate beryllium hydroxide in the granular or a-form. The next stage is the con- 
version of the hydroxide into ammonium beryllium fluoride from which beryllium 
fluoride is obtained by heating and is ready for the next stage, reduction to the metal. 
A full account of the sulphate method for extracting beryllium from beryl is given 
by C. W. Schwenzfeier Jr. in " The Metal Beryllium," 1955. 

In the fluoride process as described by H. C. Kawecki, the ore, ground to pass 
70-mesh, is mixed with sodium ferric fluoride, sodium fluosilicate and soda ash; this 
mixture is briquetted and fired in a tunnel kiln at about 750°C. for two hours. The 
sintered briquettes are crushed and leached with water and the resultant solution 
treated with caustic soda to precipitate the beryllium as hydroxide, which is then 
washed and calcined at 1,000° C. The beryllium oxide so produced can be used for 
making beryllium-copper master alloy by mixing it with carbon and copper and 
reducing in an arc furnace. To obtain beryllium metal, or its alloy with aluminium, 
the oxide is converted to the fluoride which can be used for the production of the 
metal as described below. 

Metallic Beryllium. So far as can be ascertained, no completely pure beryllium is 
being produced on a commercial scale. The Brush Beryllium Company of Cleve- 
land, Ohio, U.S.A., produce a " structural grade block " of the following percentage 
composition: beryllium, 98-5 min.; beryllium oxide, 1-2 max.; aluminium, 014 
max.; carbon, 012 max.; iron, 016 max.; magnesium, 008 max.; silicon, 010 
max.; other metallic impurities, 04 max. The material has a minimum density of 
1 -84 g./c.c, ultimate tensile strength 35,000 p.s.i. min., yield strength (0-2 per cent, 
offset) 27,000 p.s.i., and elongation (per cent, in 1 in.) 1 min. 

Although several processes for the reduction of beryllium compounds to the 
metal have been used on a small scale, it would seem that for the production of high 
purity beryllium the Brush Beryllium Company's process, based on the reduction of 
the fluoride by magnesium, is the most appropriate. The starting point may be 
ammonium beryllium fluoride (NH 4 )2BeF 4) which on heating to 900-1, 100°C. 
yields a glassy beryllium fluoride and ammonium fluoride gas. The beryllium fluoride, 
in the form of small pellets, is mixed with small lumps of magnesium in about one 
inch cubes and the mixture is reduced in a graphite crucible heated in a high fre- 
quency electric furnace. When the reaction is complete the melt is poured into a 
graphite receiving crucible and allowed to cool. The mixture of slag and beryllium 
pebbles is wet milled in a ball mill. About 60 per cent, of the beryllium in the charge 
is recovered as metal, the remainder passing to the milling solution, which is further 
treated. The beryllium pebbles, which may contain as much as 1 -5 per cent, mag- 



nesium, need further purification and consolidation, and this is effected by heating 
in vacuo under a suitable slag to produce ingot metal. The ingot has a large grain 
size and poor workability, and cannot be rolled or extruded directly but has to be 
reduced to a fine powder which can be sintered in vacuo to produce the various 
shapes required for processing into plant. A general account of the fabrication of 
beryllium by powder metallurgy has been given by W. W. Beaver, 1955. 

According to C. W. Schwenzfeier Jr., an analysis of typical vacuum cast ingot 
shows a minimum percentage of beryllium of 99-5 and the following amounts of 
impurities in parts per million: carbon 400, iron 1,100, manganese 70, chromium 90, 
nickel 130, magnesium 500, aluminium 600, boron 1 -2, cadmium < 0-5, lithium < 1, 
silver < 5, cobalt < 2. 

In a process used at the Avonmouth Works of the Imperial Smelting Corpora- 
tion, according to L. J. Derham and D. A. Temple, 1957, beryllium hydroxide is 
reacted with ammonium bifluoride and the resultant ammonium fluoberyllate is 
crystallized out by evaporation, separated and decomposed by heating in a graphite 
retort to 850°C. The ammonium fluoride is sublimed from the retort, collected and 
returned to the system and the beryllium fluoride remaining is tapped off as a 
molten anhydrous glass into graphite moulds. After crushing, the beryllium fluoride 
is mixed with high purity magnesium and reduced in a graphite crucible at 900°C. 
The charge is then heated to above 1,280°C. the molten beryllium is separated and 
later refined by the vacuum method, yielding a beryllium ingot containing the 
following average amounts of impurities in parts per million: boron, < 1; cad- 
mium, < 1; lithium, < 1; nickel, 20; chromium, 20; manganese, 70; lead, < 20; 
aluminium, 250; copper, < 50; silicon, 200; iron, 200-300. 

The Imperial Smelting Corporation, the U.K. subsidiary of the Consolidated 
Zinc Corporation, and the Beryllium Corporation of Reading, Pennsylvania, 
U.S.A., have formed an equally owned British company called Consolidated 
Beryllium Ltd., which is to produce, at Avonmouth near Bristol, nuclear grade 
beryllium and beryllium-copper master alloy. The new company is planning the 
largest beryllium metal plant in the world. It is estimated that the U.K. require- 
ments for metallic beryllium may reach 100 tons per annum by 1965. 

A process used at the British Government's Milford Haven plant operated by 
Murex Ltd., as described by T. S. Bryant, consists in mixing the finely ground ore 
with sodium silicofluoride, soda ash and water, briquetting and heating in a tunnel 
kiln at about 780°C. The reaction which occurs is represented by the equation 

3BeO.Al 2 3 .6Si0 2 + 3Na 2 SiF 6 = 2 A1F 3 + 3BeF 2 + 6NaF + 9SK) 2 

The briquettes after cooling are crushed, lixiviated with water and the solution, 
which carries the beryllium, separated and treated with caustic soda solution to 
precipitate crude beryllium hydroxide. This latter, which contains some ferric 
hydroxide, silica and sodium fluoride, is separated, redissolved in caustic soda, the 
solution filtered and the liquid treated with steam, which causes the precipitation of 
granular beryllium hydroxide. This product is washed, dried, mixed with carbon 
and coal tar and pressed into briquettes, which are then chlorinated to produce 
beryllium fluoride, which after further purification is electrolyzed in a nickel cell 



using a cathode of sheet nickel and a graphite anode, at a temperature of about 

The physical properties of pure metallic beryllium are as follows: 

Atomic number . . . . . .4 

Atomic weight 

Crystal structure . 

Melting point 

Density at room temperature 

Thermal conductivity (at 20°C.) 

Thermal neutron absorption cross-section: 

Microscopic ..... 

Macroscopic ..... 

Specific heat at room temperature . 

Coefficient of linear expansion (at 25-1 00°C.) . 

Young's modulus . . . . . 

♦lbarn = 10- 24 cm. : 

9 02 

hexagonal close-packed 

1,283 °C. 

l-85g./cm. 3 

0-066 lb./in. s 


009 ± 005 barn*/atom. 
0012 cm.- 1 
0-42 cal./g./°C. 
11-54 x 10- 6 per°C. 
43 x 10 6 lb./in. a 

Beryllium is a difficult metal to process owing to its toxicity and brittleness, but 
extrusion methods have been used successfully to produce bar, tube and simple 
shapes. Hot working of the metal in sheaths is the most common method of pro- 
ducing wrought beryllium. The metal is not easy to machine, although with care 
high finish machined components can be obtained. 

Nuclear Reactor Uses. Fuel in a nuclear reactor releases neutrons at high 
velocity and it is often necessary to slow them down to energies where the chain 
reaction can be made more effective. It is therefore customary to include in the 
reactor a moderator, or slowing down substance, the most effective materials for this 
purpose being elements of low atomic weight, as their mass more nearly approxi- 
mates to that of the neutrons. To be effective, the element selected must have a low 
neutron cross-section absorption, so that it does not capture or absorb many neu- 
trons and so make them unavailable for striking fuel atoms. Beryllium is the 
metallic element most suitable as a moderator. 

The properties of beryllium also make it a promising fuel-canning metal for use 
in gas cooled nuclear reactors. In particular its melting point is higher than those of 
other metals previously used for this purpose; it has good resistance to oxidation by 
wet or dry carbon dioxide at high temperatures and it has low neutron cross- 
section absorption. For these and other reasons the United Kingdom Atomic 
Energy Authority is using beryllium fuel cans in its Advanced Gas Cooled Reactor 
in which a surface temperature of the fuel element as high as 600° C. is reached. In 
general, however, beryllium has poor resistance to high temperature water and 
liquid metals under the conditions likely to be encountered in power reactors, but 
much depends upon the purity of the metal and the conditions of service. The 
Metals Division of Imperial Chemical Industries Ltd. is operating the first plant 
in Europe to produce wrought beryllium. 



Radium-beryllium neutron sources are being used in the Zenith (zero energy 
high temperature) research reactor being built at the U.K. Winfrith Heath Atomic 
Energy Establishment. 


The principal use for commercial beryl is as a source of metallic beryllium, 
which reaches the market mostly in the form of copper alloys containing about 2 
per cent, of beryllium. These alloys, after suitable heat treatment, develop a high 
tensile strength and ability to withstand repeated stress. 

As a general rule, purchasers of commercial beryl for use in the production of 
beryllium alloys specify that it shall contain not less than 10 or 12 per cent, of 
beryllium oxide (BeO). 

U.S. National Stockpile Specification P-6-R1, dated October 25th, 1954, for the 
purchase of beryl for the manufacture of beryllium metal, beryllium chemicals or 
beryllium-bearing alloys, requires the mineral to contain not less than 10 per cent, of 
beryllium oxide, BeO. The ore may be in the form of either hand-sorted material or 
flotation concentrates. 

The so-called 4 per cent, beryllium-copper master alloy, which may range in 
beryllium content between 3-75 and 4-40 per cent., is used for deoxidizing and 
desulphurizing copper, nickel or steel, or in making casting alloys. 
' When small amounts of beryllium are added to copper, an alloy is produced 
which, by appropriate heat treatment, develops a hardness equal to that of fairly 
hard steel. Such an alloy, known as " Cu.Be.250," as produced in Great Britain, 
contains about 2 per cent, of beryllium and 0-25 per cent, of cobalt, the remainder 
being copper. This alloy is claimed to be particularly suitable for spring parts, cams, 
t appet bearings, swit ch blades, etc., owing to its high tensile strehgthThardness and 
absence of elastic creep. The alloy is non-magnetic and is also used for making 
non-sparking safety hand tools which are claimed to have a much longer life than 
the phosphor-bronze tools usually employed when non-sparking properties are 

The U.S. National Stockpile Specification P-94-R of September 8th, 1954, 
covers beryllium copper, generally known as 4 per cent, beryllium copper master 
alloy, and requires that it shall have the following percentage chemical composition 
by weight: Beryllium 3-75 (min.) to 4-50 (max.); Iron (max.) 015; Aluminium 
(max.) 013; Silicon (max.) 015; Tin (max.) 003; Lead (max.) 001 ; Nickel (max.) 
005; Chromium (max.) 002; Cobalt (max.) 010; Zinc (max.) 003; total other 
elements (max.) 05 ; Copper balance. 

The American Society for Testing Materials have issued several specifications 
for copper-beryllium alloys. Specification B 194-55 for alloy-plate, sheet, strip, and 
rolled bar, requires a beryllium content between 1 -8 and 2-05 per cent., with the 
following limits for additive elements : nickel or cobalt (or both), min. 0-2 per cent. ; 
nickel plus cobalt plus iron, max. 0-6 per cent.; copper plus beryllium plus additive 
elements, min. 99-5 per cent. The same chemical composition is also required for 
beryllium-copper alloy wire (B 197-52). 

According to J. R. Burns, the addition of beryllium to the extent of 0001 per 



cent, or more to magnesium alloys produces a marked reduction in the tendency of 
the alloys to burn and may actually increase the ignition temperature by as much as 
400° F. Alloys containing beryllium may be held molten without fluxes and success- 
fully cast in foundry sand containing no inhibitors. Beryllium additions are also 
stated to be effective in precipitating iron and manganese from the magnesium 
melt. The amount of beryllium added, usually in the form of a beryllium- 
magnesium-aluminium master alloy, ranges from 0001 to 001 per cent. Since 
beryllium adversely affects the grain size in magnesium alloys, small additions of 
titanium or zirconium may be desirable to inhibit grain growth when the beryllium 
content exceeds 005 per cent. 

A recent introduction is a series of beryllium-nickel casting alloys containing 
between 20 and 2-8 per cent, beryllium, a maximum of 0-40 per cent, of carbon, no 
chromium and the balance nickel. The composition of some beryllium-copper 
casting alloys; made by the Brush Beryllium Co. of Ohio, are shown in Table 30. 

Table 30 

Beryllium-Copper Casting Alloys* 


Per cent. 

Per cent. 

Per cent. 

Per cent. 

Per cent. 

Beryllium . 


1-40-1 -60 









*From the Brush Beryllium Company, Ohio, U.S.A. 

Alloy 35-C is high conducting, and suitable for resistance welding, dies and 
electrodes. Alloy 10-C is claimed to be suitable for components requiring good 
conductivity with moderate strength and hardness. It is stated to give good service 
up to 700°F. with no appreciable loss of hardness. Alloy 20-C is described as the 
standard beryllium-copper casting alloy. Among copper based casting materials 
alloy 240-C is claimed to have the highest strength. Alloy 275-C is a special purpose 
foundry alloy designed for plastic moulds and other applications requiring maximum 
strength, hardness and wear resistance. 

Small additions of beryllium, which may be made in the form of beryllium- 
aluminium (5 : 95) or beryUium-magnesium-aluminium master (5:5: 90) alloys, 
are stated to have proved beneficial in the melting and processing of wrought and 
cast aluminium alloys. Over 01 per cent, beryllium serves as a hardener, whilst 
lesser amounts improve fluidity and corrosion resistance. 

Beryllium has been used in Germany in alloys for watch and clock springs. 
One such material, known as " Contracid ", is composed of nickel, 50 per cent.; 
chromium, 15 per cent.; molybdenum, 7 per cent.; iron, 15 per cent.; manganese, 
2 per cent., with 0-5-0-75 per cent, of beryllium. 

Beryllium foil of a thickness of about 016 mm. can be produced in malleable 
form by evaporating the metal at high vacuum by electronic bombardment and 



condensing it on the walls of a pyrex tube. Such metal is stated also to be suitable 
for the production of X-ray windows. 

Small quantities of beryl are used in the chemical industry for the manufacture 
of beryllium salts and in ceramic work. 

Refractory Uses. Considerable attention has been given in recent years to the 
possibilities of beryllium oxide as a refractory for special ceramic, electrical and 
mechanical purposes. The characteristics which make it of value for such purposes 
are its high melting point (2,570°C), density (3 025) and resistance to attack by 
many chemicals except hydrofluoric acid, fused alkali and water vapour at high 
temperature. Normal ceramic technique usually requires a high-fired dense oxide; 
ceramic bodies may consist of about 90 per cent, beryllium oxide, the remainder 
being alumina or zirconia. 

Beryllium carbide has been used to a small extent as a refractory as also have 
cermets containing beryllium oxide and a metallic powder. 

Beryllium oxide is no longer used for the preparation of zinc-beryllium silicate 
as a phosphor for coating fluorescent lighting tubes and screens. It is replaced by the 
non-poisonous calcium halophosphate. The oxide and carbonate, activated by uran- 
ium salts or rare earths, are used in luminescent paints. 

For ceramic work, in which beryl may be used either as a glaze or in the body, the 
mineral should carry not less than 10 per cent, of the oxide. The content of soda and 
potash, usually between 0-5 and 2-5 per cent., is not of importance unless the 
mineral is to be used for special purposes, such as in the manufacture of porcelain 
having high electrical resistance and resistance to mechanical shock. 

Toxicity of Beryllium and its Compounds. Finely divided beryllium and some of 
its compounds can produce acute chemical pneumonitis, which is similar to that 
which results from exposure to phosgene, nitrous fumes or cadmium oxide. In 
acute cases death may result. Some years ago cases were reported from the 
fluorescent lamp industry and the use of beryllium phosphors was therefore stopped. 
Acute pneumonitis has been produced by inhaling beryllium metal, oxide, sulphate, 
fluoride, hydroxide and chloride. No cases seem to have been reported of toxicity 
resulting from the handling of beryl ore or copper alloys containing less than 2 per 
cent of beryllium. The U.K. Atomic Energy Authority in order to eliminate pos- 
sible risks arising from the toxic properties of metallic beryllium has adopted a 
standard for its laboratories and workshops which requires that the average atmo- 
spheric concentration of beryllium must not exceed 2 x 10~ 6 g. per cu.m. through- 
out the working day. A laboratory for handling beryllium conforming to the above 
requirement has been designed and erected by the General Electric Company at 
their Atomic Energy Division at Erith, Kent, which conducts research on the 
metallurgy and technology of beryllium. 


" Beryllium and Beryl." By A. V. Petar. U.S. Bur. Mines, Inform. Circ. No. 6190, 1929, 20 pp., 

including bibliography. 
" Beryllium and Beryl." Anon. Min. Indus, of Br. Empire and Foreign Countries, Imperial Institute, 

Lond., 1931, 26 pp., including bibliography. 
" Beryl and Ceramics." By D. W. Luks. Foote-Prints, 1937, 10 (No. 1), 1-11. 



" Beryllium: Occurrence, Mining, Extraction, Metallurgy." Science Library Bibliogr. Ser. No. 

313 (1931-36), Lond., 1937 (134 references). 
" Miscellaneous References on the Extraction and Metallurgy of Beryllium, 1928-1937." Science 

Library Bibliogr. Ser. No. 379, Lond., 1938 (225 references). 
" Beryllium (History, Chemistry, Occurrence and Uses)." By D. C. McLaren. Mining Mag., 

1943, 69, 273-82. 
" The Metallurgy and Uses of Beryllium-Copper Alloys. 1938-1948." Science Library Bibliogr. 

Ser. No. 605, Lond., 1944 (85 references). 
" Extractive Metallurgy of Beryllium." By W. J. Kroll. U.S. Bur. Mines, Inform. Circ. No. 7326, 

1945, 15 pp. 
" Production of Beryllium and Beryllium Oxide at Degussa Plants." By W. B. C. Perrecoste. 

B.I.O.S. Final Rep. No. 319, Item 21, 1945, p. 13. 
" The Beryllium Industries of Germany and Italy (1939-1945)." F.I.A.T., Final Rep. No. 522, 

1946, 102 pp. 
" The Production of Beryllium Oxide and Beryllium-Copper." By B. R. F. Kjellgren. Trans. 

Electrochem. Soc, 1946, 89, 248-261. 
" Investigations of Beryllium Production in Germany and Italy, including production and uses of 

oxides and alloys." B.I.O.S. Final Rep. No. 550, Item 21, 1946, 81 pp. 
" Extraction and Uses of Beryllium in Germany." By G. T. Motock. U.S. Bur. Mines, Inform. 

Circ. No. 7357, 1946, 12 pp. 
" Pure Beryllium Oxide as a Refractory." By F. H. Norton. /. Amer. Ceram. Soc, 1947, 30, 

" Beryllium and Beryllium Bronze." By R. Gadeau. Microtecnic, 1947, 1, 43-46, 69-71, 85-89, 

" The Heat Treatment and Properties of some Beryllium-Nickel Alloys." By W. Lee Williams. 

Trans. Amer. Soc. Metals., 1948, 40, 163-179. 
" Beryllium in Magnesium Casting Alloys." By J. R. Burns. Trans. Amer. Soc. Metals, 1948, 40, 

" Beryllium in Industry." By H. Manley. Mine and Quarry Engng., 1948, 14, 183-90 
" The Production of Beryllium." By B. R. F. Kjellgren. /. Electrochem. Soc, 1948, 93, 122-28. 
" The Rarer Metals." By J. de Ment, H. C. Dake and E. A. Roberts. Lond., 1949 (Beryllium, 

pp. 1-15.). 
" Powder Metallurgy of Beryllium." By H. H. Hauser and N. P. Pinto. Trans. Amer. Soc. Metals, 

1950, preprint No. 38, 18 pp. 
" A Review of Beryllium and Beryllium Alloys." By J. T. Richards. /. Metals 1951, 3 (May), 

" Beryllium: Materials Survey." U.S. Bur. Mines (prepared for the National Security Resources 

Board), September, 1953, 178 pp. 
" Magnesium Alloy Permanent and Semi-permanent Mold Castings." By M. E. Gantz, Jr., 

E. M. Gingerich and R. T. Wood. Trans. Amer. Foundrymen's Assoc, 1953, 61, 502-9. 
" The Role of Beryllium in Atomic Energy Projects." By R. E. Pahler. Metal Progr., 1954, 65, 

" Preparation, Properties and Uses of Beryllium." By E. J. Boyle and J. L. Clegg. Nuclear Eng., 

Pt. 1, Chem. Engng. Prog. Symposium, 1954, pp. 53-6. 
" The Metal Beryllium." Ed. by D. W. White, Jr. and J. E. Burke. American Society for Metals, 

Cleveland, Ohio, 1955, 703 pp. 
" The Physical and Mechanical Properties of Beryllium Metal." By D. W. Lillie. ibid., pp. 

" The Nuclear Properties of Beryllium." By J. R. Stehn. ibid., pp. 328-366. 
" Health Hazards from Beryllium." By M. Eisenbud. ibid., 620-640. 
" The Fabrication of Beryllium by Powder Metallurgy." By W. W. Beaver, ibid., 152-201. 
" Refractory Compounds and Cermets of Beryllium." By W. W. Beaver, ibid., 570-597. 
" The Preparation of Beryllium Metal by the Thermal Reduction of the Fluoride." By L. J. 

Derham and D. A. Temple. From " Extraction and refining of the Rarer Metals." Inst. Min. 

Met., 1957, pp. 323-336. 
" Beryllium Production at Milford Haven." By P. S. Bryant, ibid., pp. 310-322. 
" Beryllium in Industry: Some Medical Implications." By E. E. Lieber. Chem. and Ind., 1958 

(May 3), 508-9. 
" Beryllium." By Pierre Silber, Nouveau Traite de Chimie Minerale, Ed. by P. Pascal. Pans, 

1958, Vol. IV, pp. 7-134. 
" Beryllium for Structural Applications, a Review of the Unclassified Literature." By N. Hodge. 

Defense Materials Information Center, Battelle Memorial Inst. D.M.I.C. Rept. 106, 1958, 

178 pp. 
" Report of the Panel on Beryllium." Materials Advisory Board, Nat. Acad. Sci. Nat. Res. 

Council, Washington, D.C., MAB— 129— M, 1958, 90 pp. 
" Beryllium-Nickel Data Sheet," No. 1. Brush Beryllium Co., 1958, 2 pp. 
" Beryllium-Copper Casting Ingots and Master Alloys." Bull. No. 3, Brush Beryllium Co., 1959, 

4 pp. 
" Pennrold Beryllium-Copper Alloys Data Sheets." Brush Beryllium Co., 4 pp. 
'* Beryllium." By G. E. Darwin and J. H. Buddery, Lond., 1960, 400 pp. 
" Beryllium." U.S. Bur. Mines, Minerals Yearbook (Annual). 



Standard Specifications 

American Society for Testing Materials 
A.S.T.M. Standards, 1958: 

Copper Beryllium Alloy— Plate, Sheet and Strip. B. 194-55. 

Copper Beryllium Alloy— Rod and Bar. B. 196-52. 

Copper Beryllium Alloy— Wire. B.i97-52. 
U.S. National Stockpile Specifications: 

Beryl. P-6-RI, October 25th, 1954. 

Beryllium-Copper Master Alloy, P-94-R, September 8th, 1954. 


Bismuth occurs in nature as the metal and, combined with other elements, as the 
sulphide, bismuthinite (Bi 2 S3), which contains up to 81 per cent, of bismuth; as 
bismutite, a basic carbonate of variable composition, which may contain up to 80 
per cent, of bismuth, and as bismite, or bismuth ochre, with up to 90 per cent, of 

Rich deposits of these minerals are uncommon and most of the world's supply 
of bismuth is obtained from the treatment of lead and copper refinery slimes, and 
as a by-product from the mining and treatment of gold, tin and tungsten ores. 

As bismuth ores are mostly rather brittle, it is difficult to prevent them sliming 
during the dressing of other ores with which they occur associated. A number of 
concentrating processes, including magnetic separation, concentrating tables and 
flotation, have been used on ores which contain enough bismuth to make it worth 
while to attempt a separation of the bismuth ore before smelting the other metals 

The refining of lead and copper is the source of most of the bismuth recovered 
in the United States, but in Canada the metal is chiefly recovered from the treatment 
of silver-lead, silver-cobalt ores and molybdenite ores. Bismuth is being obtained by 
the Molybdenite Corporation of Canada from ore obtained at La Come, Quebec, 
which carries 0-51 per cent, molybdenite and 0035 per cent, bismuth. By flotation a 
concentrate is obtained containing 80 per cent, molybdenite and 10 per cent, 
bismuth, from which the bismuth is separated by leaching with hydrochloric acid. 
Most of the metal obtained in Peru is recovered in the treatment of lead ores, but in 
Bolivia the bismuth is found associated with tin ore, while in Australia the element 
occurs chiefly associated with tin, tungsten and molybdenum ores. 

World Production 

Varying amounts of bismuth are obtained from over a dozen countries, the chief 
being Mexico, Peru, Korea, Canada, Yugoslavia, France, Bolivia, Spain. It is 
difficult to arrive at an accurate estimate of the world's annual output, but it is 
probably about 50,000 cwt. of contained bismuth. 

During World War II, Canadian production rose from about 85 cwt. to a peak 
of 3,639 cwt. in 1943 and totalled 3,680 cwt. in 1958. The United States output 



probably reached a maximum of about 1,350 cwt. in 1942. Peru attained a peak 
production of 9,506 cwt. in 1943, but, the output has fallen to almost one-third this 
quantity in recent years owing to a decrease in the percentage of bismuth in the lead 
ore smelted. Bismuth is exported from producing countries in various forms, e.g. 
ore, concentrates, metal, in lead bullion and matte. 

Imports into Great Britain, which totalled 5,104 cwt. in 1938, rose to 9,015 cwt. 
in 1942, and in 1958 imports (less re-exports) included 8,140 cwt. of bismuth 
and 2,560 cwt. of bismuth alloys containing more than 50 per cent, of bismuth. 
Exports (domestic produce) in 1958 totalled 6,460 cwt. of bismuth and 3,400 cwt. of 
bismuth salts. 

A smelter and refinery, having a monthly capacity of 150,000 lb. of refined 
bismuth, is operated by Mining and Chemical Products Ltd. at Alperton, Middlesex. 
The material treated includes bismuth ores from Bolivia, Australia and Africa; 
bismuth-lead bullion from copper refining in North America, and crude metal from 
various sources. The refined bismuth produced is of two grades: 99-99 per cent, 
purity suitable for making pharmaceutical compounds and for other purposes; and 
a high purity metal of 99-999 per cent., or better, for semi-conductor applications. 

The largest consumers of bismuth are Great Britain, the United States and 

Metallurgy of Bismuth 

When high-grade carbonate or sulphide ore is available, it is smelted with an 
alkaline flux. Ores containing much arsenic or antimony are sometimes roasted at 
low temperature to volatilize as much as possible of these constituents. 

Bismuth occurring with tin ore may be extracted by leaching with hydrochloric 
acid, and the metal recovered either as oxychloride by diluting the acid extract with 
water, or as a metal sponge by precipitation on scrap iron. The oxychloride is 
reduced to metal by smelting with an alkaline flux. 

When it occurs in lead or copper ores, on smelting practically all the bismuth is 
collected in the metals. In the electrolytic refining of crude copper any bismuth 
present (together with several other metals) accumulates in the anode slimes, from 
which it is recovered mainly by chemical processes. 

In the case of lead ores, when the metal undergoes the usual softening and de- 
silvering processes, the lead retains all the bismuth, the removal of which can be 
effected by a variety of processes, depending upon the percentage present. 

The two most important processes for recovering bismuth from lead are: (1) 
the Betts electrolytic process in which lead anodes are treated in a bath of molten 
lead fluorosilicate and fluorosilicic acid, bismuth, with other impurities, collecting 
in the anode slimes, (2) the Betterton-Kroll process which is based principally on 
the formation of high-melting compounds such as Ca2Bi2 and Mg3Bi2, which 
separate from the bath in the dross. 

The impure metallic bismuth yielded by the above methods needs refining, as it 
may contain from 3-5 per cent, of lead, with smaller amounts of tin, antimony, 
arsenic, selenium, tellurium, silver, sulphur and gold. 

The refining of the crude bismuth is a somewhat involved process, the details of 



which are dependent to some extent on the amounts of the impurities present. 
Descriptions of such processes in use in Great Britain will be found in the paper on 
" The Refining of Bismuth," by A. R. Powell, quoted in the Bibliography. Pure 
bismuth is a greyish-white metal with a brilliant lustre, and has a specific gravity of 
10-55 when molten and 9-82 when solid. It is one of the most diamagnetic of the 

Some of the physical properties of bismuth are as follows: 

Atomic number . 
Atomic weight 
Melting point 
Boiling point 
Specific heat (at 20C°.) 
(at 271°C.) 
Electrical resistance (at 0°C.) 
(at 300°C) 
Brinel hardness 
Neutron absorption cross-section for neutrons of 

velocity 2,200 m./sec 

Neutron scattering cross-section for thermal neutrons 


271 -3°C. 


0294 cal./g./°C. 

00340 cal./g./°C. 

106-8 microhms/cm. 

128-9 microhms/cm. 

lOOkg.-lOmm. ball = 




The largest use for bismuth is in pharmaceutical products, but its employment in 
so-called fusible or low-melting point alloys is increasing. 

The percentage consumption of bismuth in the United States by uses, in 1958 
was: fusible alloys 38-5, other alloys 16-7, pharmaceuticals 340, experimental 
uses 7-8, other uses 3, the total consumption being 1,242,700 lb. 

The U.S. National Stockpile Specification P-7 of October 3rd, 1951, for the 
purchase of bismuth suitable for use in the manufacture of alloys, solders or salts, 
requires a minimum of 99-99 per cent, bismuth and that the metal shall be suitable 
for the production of bismuth salts which will conform to the requirements of the 
U.S. Pharmacopia. 

Pharmacy. Manufacturers of bismuth compounds for use in pharmacy generally 
use bismuth (99-99 per cent. Bi), as the raw material. The metal should have a silver 
content of less than 001 per cent., arsenic less than 0002 per cent., and lead less 
than 0-01 per cent. 

About 70 per cent, of the world's production of bismuth is used medicinally in 
the form of the sub-carbonate, sub-nitrate, sub-gallate or aluminate in indigestion 
remedies, cosmetics, ointments and dusting powders, and for the treatment of ulcers, 
venereal disease, etc. 

Alloys. If bismuth is added to other metals, the resultant alloy melts at a lower 
temperature than either of its components and for this reason bismuth is useful for 
the production of many, so-called, fusible alloys. In the case of mixtures in the 
proportions necessary to form the eutectic alloy, the product changes from the 



solid to the liquid state at a constant temperature. Many other alloys, however, do 
not melt sharply and pass from the solid condition to a pasty mass and then to a 
completely molten mass. 

One group of bismuth-containing alloys is based on the ternary eutectic con- 
taining 15-5 per cent, of tin, 52-5 per cent, of bismuth, 32 per cent, of lead. These 
alloys melt around 96°C. and are represented commercially by Rose's, Newton's 
and D'Arcet's alloys. The alloys known as Wood's, or Lipowitz's, are representative 
of a group based on a quaternary eutectic which melts at about 70°C. and contains 
49-5 per cent, of bismuth, 1313 per cent, of tin, 27-27 per cent, of lead, and 1010 
per cent, of cadmium. 

In addition, a number of non-eutectic bismuth alloys, which melt over a range 
of temperature, are also used industrially and much useful information on these 
products has been collected by the Tin Research Institute in a publication entitled 
" Fusible Alloys Containing Tin." 

Binary alloys of bismuth and antimony all expand when passing from the 
molten to the solid state and for this reason they are useful components of type 

The compositions of some alloys containing large percentages of bismuth, are 
given in Table 31. 

Table 31 

Composition of Some Bismuth Alloys 

Per cent. 






Fusible alloys : 

Lipowitz's alloy (m.p. 73° C.) . 






Wood's metal (m.p. 72° C.) 




. — . 


Rose's metal (m.p. 100° C.) 






Cliche metal (for sprinklers) 






Pewterer's solder 










>S 5, ... 






Fusible alloys play an important part in automatic safety devices, such as fire 
alarms, automatic sprinklers, boiler safety plugs and heating equipment. In Great 
Britain a widely used sprinkler head contains Wood's metal, and is known as 
155° F. pattern. Wood's metal, although not a true quaternary, approximates fairly 

During World War II a large demand arose for low-melting alloys for filling 
thin-walled metallic tubes before bending. These were mostly alloys of bismuth, lead, 
tin and cadmium, which have fairly low melting points, well below that of boiling 
water. One alloy used extensively was Lipowitz's metal, which melts at 73°C. and 
expands slightly on solidification. This method is extensively used for bending 
aluminium tubes used in aircraft construction, and also in making hollow articles of 



sterling silver. The process has the advantage that the filling material can be easily 
and cleanly removed after the article has been bent to shape. 

Many fusible alloys, particularly Wood's metal, are able to " wet " glass and can 
be safely used to make vacuum-tight joints in glass apparatus and joints between 
metal and glass. 

Some alloys containing bismuth, lead and tin are used for tempering steel tools. 
An alloy containing bismuth, 8 parts; lead, 6 parts; and tin, 3 parts, melts at about 
100°C. and it is possible to obtain a series of alloys melting up to about 177° C. by 
increasing the proportions of lead and tin to bismuth. 

Bismuth is an essential component of an interesting product known as " matrix 
alloy," which carries about 47 per cent, of bismuth, 28-5 per cent, of lead, 14-5 per 
cent, of tin, and 9 per cent, of antimony. The alloy becomes fluid at about 103° C, 
but is not completely molten until a temperature of about 227° C. is reached. The 
alloy does not shrink on solidification, has a Brinell hardness of 19 and is very 
resistant to deformation. Matrix alloy is used to mount the different parts of complex 
dies and punches for drilling. Its melting point is low enough not to endanger the 
temper of the tools and, when the latter are worn out, the alloy can be salvaged for 

Alloys of the " Cerromatrix " type are extensively used in aircraft assembly jigs, 
as moulds for cold-forming plastics and for pressing " plastic wood " and fibre in 
the manufacture of imitation wood carvings. 

An interesting alloy approximating in composition to MnBi has been developed 
by the American Westinghouse Co. Ltd. The alloy is claimed to be suitable for 
use in permanent magnets which have unusual resistance to demagnetization and 
therefore are not adversely affected by external magnetic fields. The alloy in powder 
form is incorporated in a plastic binder and so the magnet can be easily tapped, 
drilled or cut. 

Some bismuth alloys, such as Malottes metal, are used in the manufacture of 
dentures, and " Cerrodent " is used in making models. 

An interesting cooling unit employing bismuth has been developed in the United 
States. The unit is based on the Peltier-Seebeck effect, a phenomenon which causes 
different temperatures to develop in two metals when an electric current is passed 
through their junction, in this case the junction is bismuth-tellurium. 

Surgical syringes are frequently assembled with an alloy containing 27 per cent, 
of bismuth, 44 per cent, of tin, 28 per cent, of lead and 1 per cent, of antimony. 

During recent years considerable attention has been given to the possibilities of 
bismuth in atomic energy projects. A solution of uranium in metallic bismuth has 
been investigated as a fuel for an externally cooled reactor and a dispersion of a 
uranium-tin compound (USn3> in lead-tin-bismuth alloys for an internally cooled 
reactor. A thorium-bismuth compound (ThaBis) dispersed in bismuth-lead has been 
suggested for a breeder blanket in both the above-mentioned forms of reactor design. 

Bismuth is used to a small extent in the preparation of certain phosphors and in 
the manufacture of selenium current rectifiers. A newly developed British invention 
known as the " Standfast " machine uses a bath of molten bismuth alloy as a colour 
fixation medium for the continuous vat dyeing of textiles. 




" Bismuth Ores." By R. Allen. Monographs on Mineral Resources with Special Reference to the 

British Empire. Imperial Institute, Lond., 1925. 62 pp., including bibliography. 
" Bismuth." By W. C. Smith. " Handbook of Non-ferrous Metallurgy." Ed. by D. M. Liddell, 

Lond., 1945, pp. 139^13. 
" Bismuth." By N. H. Fisher and N. H. Ludbrook. Miner. Res. Australia, Sum. Rep. No. 9, 

Canberra, 1946, 27 pp., including bibliography. 
" Bismuth in Works By-products." By C. C. Downie. Min. J. (Lond.), 1947, 229, 403-04. 
" The Refining of Bismuth." By A. R. Powell. " The Refining of Non-ferrous Metals." Inst. Min. 

Met. (Lond.), 1949, 245-253. 
" Bismuth." By H. H. Howe in " Rare Metals Handbook," Ed. by C. A. Hampel, New York, 

1954. 657 pp. (Bismuth pp. 57-69). 
" Liquid Metal Fuels." By R. J. Teitel, D. H. Gurinsky and J. S. Brymer. Nucleonics, 1954, 12, 

(No. 7), 1415. 
" Corrosion Problems with Bismuth-Uranium Fuels." By R. J. Weeks, C. J. Kalmut, M. 

Silberberg, W. E. Miller and D. H. Gurinsky. Peaceful Uses of Atomic Energy, United 

Nations, 1955, Vol. IX, pp. 341-355. 
" Distillation of Liquid Metal (Bismuth) Reactor Fuel." By F. S. Martin and R. E. Brown. 

Atomic Energy Research Establishment, 1957, C/R2391, 12 pp. 
" Bismuth." By Louis Domange. Nouveau Traite de Chimie Minerale, Ed. by P. Pascal. Paris, 

1958, Vol. XI, pp. 665-836. 
" Bismuth." U.S. Bur. Mines, Minerals Yearbook (Annual). 

Standard Specification 

U.S. National Stockpile Specification: 

Metallic Bismuth (suitable for use in the manufacture of alloys, solders and salts). P-7. 
October 3rd, 1951. 


The boron compounds of commerce may occur in nature either as bedded deposits 
of borates of sodium, calcium, or magnesium ; as boric acid in the emanations which 
result from volcanic activity; or in lake brines. 

The principal boron minerals found in deposits are kernite, or " rasorite " 
(Na 2 B 4 7 .4H 2 0), hydrated borate of sodium; colemanite (CaaB^^-SH-jO), 
hydrated borate of calcium; ulexite (Na 2 0.2Ca0.5B 2 3 .16H 2 0), hydrated borate 
of sodium and calcium, and pandermite (or priceite), the hydrated borate of calcium 
having the formula 4Ca0.5B 2 3 .7H 2 ; stassfurtite or boracite (Mg,Cl 2 B 16 O 30 ), 
and sassolite (B(OH) 3 ). Analyses of the more important of these minerals are 
shown in Table 32. 

The name " Rasorite," often used as a synonym for kernite, is a trade name 
registered internationally by Borax Consolidated Ltd. or its associates. 

Kernite supplies a large proportion of the world's demand for borates. It was also 
used during World War II for the manufacture of boric acid, but is now replaced for 
this purpose by pandermite and colemanite from Turkey (known in the trade as 
Turkish boracite) and by supplies of crude boric acid from Italy. 

Borates are also obtained in large amounts from brines in the U.S.A., notably at 
Searles Lake, California, from which potassium chloride, sodium carbonate, 
sodium sulphate, lithium compounds and other salts, are also recovered {see p. 540). 



Table 32 

Composition of Borate Minerals 


Pandermite (as 
shipped to refinery) 



Per cent. 

Per cent. 

Per cent. 

Per cent. 

Boric oxide, B a 3 





Ferric oxide, Fea0 3 . 

0-3 to 0-4 


. — . 

Alumina, Al 2 O a 




Lime, CaO 





Magnesia, MgO 





Soda, NazO . 




Sulphuric anhydride, SO s . 





Insoluble matter, SiO a 



Water, H a O . 





Carbonate, CO z 





* Water plus organic matter. 

Volcanic emanations locally termed " Soffioni," are an important source of boric 
acid in Italy. 

In recent years experimental work has been done on methods for treating the 
material from low-grade boron deposits. Some processes provide for the liberation 
of the boron as boric acid, which is subsequently recovered by flotation. 

World Production 

For many years past over 95 per cent, of the world's output of boron compounds 
has been obtained in the United States (from deposits of kernite and lake brines): 
the remainder being produced by Turkey (pandermite and colemanite), Italy (boric 
acid), Argentina (ulexite and tincal), and Chile (ulexite). The world's production of 
boron compounds has increased considerably in recent years, chiefly on account 
of the larger quantities won in the United States, which attained a peak output of 
705,758 long tons in 1954, as compared with 219,004 long tons in 1939. In most 
cases the raw material is refined to give borates or boric acid by the company 
operating the deposits, or a local subsidiary. No sources of supply of boron com- 
pounds are known in Great Britain and industrial needs are met by imports, which 
in 1958 consisted of 14,889 long tons of boron mineral, 23,708 long tons of borax, 
and 3,472 long tons of boric acid. 

Although details of production in recent years are not available, it would appear 
that the U.S.S.R. is self sufficient as regards borates. The deposits, which are stated 
to be very extensive, occur in the Inder district just north of the Ural River contain 
the boron minerals Szaybelyite (the most important), priceite, inyoite, colemanite, 
hydroborate, ulexite and some magnesium borates. 

In Turkey, the world's second largest producer of borates, the minerals occur 
principally in the provinces of Balikesir, Bursa and Kutahya. 

In South America the known borate deposits (mostly ulexite) are located in 
north-western Argentina and northern Chile, western Bolivia and southern Peru. 




Boric acid and the borates have many industrial uses, the principal of which 
include the manufacture of glass, vitreous enamels, ceramic glazes, leather, paper, 
adhesives, and explosives; as a flux in metallurgy ; in brazing and welding; launder- 
ing; for pharmaceutical and cosmetic purposes, and in the food industry. 

The percentage use of boron products in the United States is distributed roughly 
as follows: Glass, 28; porcelain enamel, 14; weed control, 10; fertilizers, 4; soaps, 
3 ; boron compounds, 3 ; antifreeze, 3 ; starch and adhesives, 2 ; insulation materials, 
2; smelters, drugs and cosmetics, iron and steel, electrolytic condensers, 1 each; 
distributors, 11 ; various miscellaneous uses, 16. 

Cleansing Purposes. A.S.T.M. Specification D 929-50 covers borax suitable for 
various washing, cleaning and scouring processes, with or without soap as conditions 
demand and where a mildly alkaline material is desired. The borax (sodium tetra- 
borate) shall be a white, crystalline powder, or colourless transparent crystals 
corresponding approximately to the formula Na 2 B 4 7 . 10H 2 0. It shall conform as 
regards chemical composition with the requirements shown in Table 33. 

Table 33 

Borax for Washing, Scouring, etc., A.S.T.M. D 929-50 

Per cent. 
Borax, NaaE^O?, (expressed as the anhydrous salt) tnin. . . 52-5 

Free acid none 

Free alkali, calculated as NaOH, max 0-25 

Matter insoluble in water, max. . . . . . .0-1 

Sieve test as specified. 

The perborates of sodium, which are used extensively in washing powders, are 
usually prepared from commercial granulated borax. Sodium perborate is marketed 
in two forms: (1) The so-called tetrahydrate, NaB0 2 .H 2 0.3H 2 0, which has an active 
oxygen content of about 10 per cent., and (2) the monohydrate, NaB0 2 .H 2 0, 
which has an active oxygen content of about 16 per cent. Sodium perborate, 
dissolved in water, dissociates and reacts in a manner similar to a mixture of 
hydrogen peroxide, boric acid and sodium hydroxide. Hence, it finds use where a 
bleaching agent in powder form is required. In the textile industry it may be used 
for treating cotton, linen, rayon, wool and other fabrics. It will also bleach certain 
waxes, ivory, glue and flour. An increasing use is in packaged household detergent 
washing powders. Sodium perborate is used for oxidizing and fixing vat dyes and 
also with some sulphur dyes. It also finds use in dentifrices, cosmetics, mouth- 
washes and certain ointments. A useful account of the properties and applications 
of the product is given in a booklet entitled " Sodium Perborate and Sodium 
Percarbonate," issued by Laporte Chemicals Ltd. of London, who are large makers 
of these chemicals. 

Glass Manufacture. In the production of ordinary glass for bottles, jars, etc., 
between 15 and 50 parts borax may be used to each 1,000 parts of sand. Borax and 
boric acid are used together in the manufacture of a number of borosilicate glasses of 



low alkali content, including laboratory ware, optical glass, ovenware, etc. Apart 
from the intrinsic properties of boric oxide needed in the finished glass, borax and 
boric acid act as fluxes and make it possible commercially to produce glasses con- 
taining high percentages of alumina and silica. Boric oxide confers a low coefficient 
of expansion, increase in resistance to mechanical and thermal shock, increase in 
refractive index, and gives a hard surface with a bright and pleasing appearance. 

Ceramic Industry. Both borax and boric acid are important constituents of 
many glazes used on china and earthenware. Borosilicate glazes have good covering 
power and are therefore economical in use. 

Borax is an important material in the preparation of vitreous enamels and may 
constitute up to 33 per cent, of such preparations. The enamels can be used at 
relatively low temperatures, have good covering power, and give coatings which are 
tough, durable and have a good finish. Sometimes anhydrous kernite concentrates 
are used for ground coat and dark coloured cover coat frits, instead of the refined 
products mentioned above. 

Leather Manufacture. A solution of borax is used to hasten the cleansing and 
softening of hides and skins, and for neutralizing the acidity of chrome tanned 
leather. Boric acid is used to neutralize and remove the lime employed for dehairing 
in the treatment of hides and skins. 

Textile Industry. Considerable quantities of borax are used for controlling the 
alkalinity of solutions used in the manufacture of rayon, in many dyeing and bleach- 
ing processes and in the degumming and scouring of natural silk and wool. A 
mixture of borax and boric acid is one of the best flame-proofing materials for 

Anti-freeze. Borax is used in the preparation of many anti-freeze mixtures, both 
in the United Kingdom and in the United States, its function in general being to 
prevent corrosion of the cooling system. 

Abrasives. Boron carbide, one of the hardest synthetic abrasives, is produced by 
heating a mixture of dehydrated boric acid and low ash petroleum coke in an electric 
resistance furnace at about 2,770° C. 

" Borazon," has the same hardness as diamond and is a cubic form of boron 
nitride, which is a good electrical insulator. It is made according to R. H. Wentorf, 
Jr. at a pressure of about 8,000 atm. and a temperature of about 1,800° C, under 
conditions attained in the so-called " Belt " apparatus of T. H. Hall. The reaction is 
complete in a few minutes and the crystals, which form spontaneously, may reach 
one carat weight in one operation. The crystals vary in size from 1 to 600 microns 
average diameter and are commonly 100 microns. 

Catalysts. Boron trifluoride, which has been produced commercially in the 
United States since 1936 and more recently in Great Britain, is being used extensively 
as a catalyst in many organic chemical reactions, such as alkylation, polymerization 
and isomerization. 

The chemical is distributed either as a compressed gas (in steel cylinders) or in 
the form of complexes with organic substances, such as acetic acid or ether. 

Dyestuffs. For use in the manufacture of dyestuffs, one large user in Great 
Britain specifies borax with not less than 99 per cent, sodium biborate decahydrate, 



Na 2 B 4 7 . 10H 2 O, only traces of chlorides or sulphates and no salts of heavy metals. 
Boric acid when used for the same purpose is required to be a white crystalline 
product containing 99-7 per cent, of boric acid, H3BO3. Maxima for impurities 
include: metallic impurities, calculated as sulphates, 05 per cent.; sulphates, 
calculated as Na2SC>4, 015 per cent., and matter insoluble in water, 01 per cent. 

Explosives. One of the largest users in Great Britain specifies that for use in 
blasting explosives, borax shall be white in colour, free from mechanical impurities 
and from salts of heavy metals and its content of moisture and combined water 
shall be not less than 45, nor more than 47-5 per cent.; chlorides, calculated as 
sodium chloride, must not exceed 015 per cent., and sulphates, calculated as sodium 
sulphate, are limited to 0-25 per cent. ; whilst matter insoluble in water must not be 
over 01 percent. 

Nuclear Uses. Elemental boron and some of its compounds have properties which 
render them of value for the shielding of thermal neutrons. Boron in naturally 
occurring compounds is a mixture of 19-57 per cent, boron-10 and 80-43 per cent. 
boron-1 1 isotopes and has an absorption cross-section for thermal neutrons of about 
755 barns, the corresponding value for the separated boron-10 isotope being 3,850 
barns. Although cadmium, which has a higher thermal neutron absorption than 
boron, is sometimes used, boron is preferable for nuclear shielding applications as 
its secondary gamma radiation is soft and the residual activity is negligible, whereas 
with cadmium the absorption of neutrons results in secondary gamma radiation. 

For the isolation of boron-10 the starting point is usually boron trifluoride, 
which is reacted with dimethyl ether and the resultant complex, on fractional 
distillation, gives most of the boron-10 in the liquid phase. 

Boron trifluoride has a freezing point of -128° C, a boiling point of -101° C, 
a critical temperature of -12-25° C. and a critical pressure of 49-2 atm. It is supplied 
by the Imperial Smelting Corporation, Ltd., who were the pioneers in fluorine 
development in Great Britain, either as a commercial gas containing not less than 
98-5 per cent, of BF 3 or as a high purity product containing about 99-8 per cent. 

In the United Kingdom isotopes of boron are prepared by 20th Century Elec- 
tronics Ltd. of Croydon, Surrey, who are prepared to supply elemental boron 
containing up to 99 per cent, of boron-10 isotope, but they state that for general 
application 90-94 per cent, is acceptable and more easily manufactured. Percentages 
as low as 50 may be useful where a compromise has to be made between enrichment 
and economy. The same firm also supplies boron-1 1 up to 99 per cent, enrichment 
for use where a minimum cross-section for neutron absorption is required. Boron 
trifluoride is supplied in breaker-seal bottles or in high pressure cylinders, and 
potassium borofluoride, KBF4, is available in crystal form. 

Boron trioxide, enriched as regards its boron-10 content is used in scintillating 
phosphors and for neutron detection. Another important use is the incorporation of 
elemental boron or boron carbide in lightweight shielding materials for nuclear 

Ammonium pentaborate (NH 4 ) a B 10 O 16 . 8H 2 0, is used as a chemical poison 
charge for the absorption of thermal neutrons for an emergency situation or for a 



shut-down period for repairs. The United States Borax and Chemical Corporation 
supply a granular product stated to comply with the requirements of U.S. Military 
Specification MIL-A-19824A (Ships). The salt is also used in electrolytic 

Anhydrous boric oxide and elemental boron incorporated in polythene are 
used for shielding. In U.S. Military Specification MIL-P-19336 (Ships), three grades 
are specified containing respectively the equivalent of 0-5, 10 and 2 per cent, 

The use of the mineral colemanite, as mined, as a constituent of concrete shield- 
ing is described in ORNL-1414 Report by Oak Ridge National Laboratory, 
U.S.A. Owing to its sparing solubility in water, colemanite is claimed to be prefer- 
able to the highly soluble sodium borates which are stated to retard the normal 
setting time of the cement. To keep the solubility of the colemanite to a minimum 
it is generally used in coarse granules which are all retained on a 100-mesh sieve. 

Elemental boron is available in both amorphous and crystalline forms, the 
latter being of much greater purity than the former. Some of the physical properties 
of elemental boron are as follows : 

Atomic number 
Atomic weight 
Melting point 
Boiling point 
Thermal neutron cross-section absorp- 
tion ...... 

Crystal structure . . . . 

Hardness, Knopp, 100 g. load 

Mohs's . . . . 
Coefficient of expansion, mean 20-750°C 


Electrical resistance at 25°C. 



19-57 per cent. B 10 ; 80-43 per cent. B 11 


approximately 3,900°C. 

Natural, 755 barns* 

B 10 isotope, 3,850 barns* 

B 11 isotope, 0-05 barns* 

tetragonal, rhombohedral and possibly 

other forms 
9-3 approximately 
8-3 X 10- 8 /°C. 
2-30-2-55 gm./cc. 
0-6 X 10 e ohm/cm. 

* 1 barn = 10- 24 cm a . 

Special borated graphite blocks, made by the Morgan Crucible Co. Ltd., are 
being used in the assembly shield which surrounds the reactor vessel at the U.K. 
Atomic Energy Authority's fast-breeder reactor at Dounreay. The purpose of these 
blocks is to slow down fast neutrons and then absorb them in the shortest possible 
distance. The blocks mostly contain 0-3 per cent, of boron, but occasionally 5 per 
cent is incorporated. 

Metallurgical Uses. Elemental boron is offered for sale by the American Potash 
and Chemical Corp o reft ion in the form of dark brown powders of the composition 
shown in Table 34. 



Table 34 

Elemental Boron: American Potash and Chemical Corporation 

Boron, B, total 
Boron, B, water-soluble 
Magnesium, Mg. 
Nitrogen, N . 
Sodium, Na . 
Insoluble in H2O2 


per cent. 



3 0-5 


004 max. 

1 -0 max. 

0-5 max. 





per cent. 

0-5 max. 

0-1 max. 

1 -0 max. 
0-5 max. 

Special High 


per cent. 

0-5 max. 

0-1 max. 

3 max. 
0-5 max. 



per cent. 

1 -0 max. 

20 max. 

1-0 max. 
0-5 max. 

Density, gm./ce. 

Average particle size, microns 

1 -0 max. 

1-0 max. 

1-5 max. 

1 -0 max. 

The composition of crystalline and amorphous elemental boron known as 
" 20-Mule Team " brand made by the United States Borax Consolidated Ltd. 
is as shown in Table 35. 

Table 35 
" 20-Mule Team " Elemental Boron— Borax Ltd. 


90-92A (R) 


Per cent 

Per cent 

Per cent 

Boron, B 


95 10 


Magnesium, Mg 




Iron, Fe ... 




Silicon, Si 




Aluminium, Al 

— . 


Manganese, Mn 




Specific gravity at 25° C. 




Amorphous boron can be used for its burning characteristics in flares, igniters 
for explosive charges and propellants. It is also useful on account of its neutron 
absorption in nuclear shielding for fixed and mobile reactors. It can be employed for 
the preparation of borides and as a component of high temperature brazing flux for 
stainless steel. 

A purchase specification for amorphous boron powder issued by the Picatinny 
Arsenal of Dover, New Jersey, designated PA-PD451 of 12th November, 1954, 
requires the material to contain a minimum of 84 per cent, of amorphous boron 
with not more than 1 -5 per cent, insoluble matter and magnesium not exceeding 
8-2 per cent. The moisture content must not exceed 0-5 per cent and the average 
particle diameter may not be more than 1 micron. 

At high temperatures, elemental boron is very reactive towards oxygen and 



nitrogen, and hence, can be used as a de-oxidizer and degasifier for certain metals. 
It may also be used to refine the grain size of some aluminium alloys and to 
facilitate the heat treatment of malleable iron and steel. 

The use of minute quantities of boron (never over 003 per cent.) to increase 
the hardenability of alloy steels was developed during World War II and a number 
of low boron alloys were marketed for use in this connection under various trade 
names, such as " Silcaz," " Carbortam," " Bortam," " Borosil." 

Boron-bearing carbon steel may be used for the sprockets of tractors. Boron is 
added to stainless steels to control corrosion and heat-resistance, and to reduce 
hot-shortness. In 1958 about 12 tons of boron was used in steel manufacture in the 
United States, as compared with about 60 tons in 1957. 

Manganese-boron, containing from 15 to 20 per cent, boron, and nickel-boron, 
with 15 to 18 per cent, boron, are also available commercially and are usually 
employed as degasifiers. 

Ferroboron is finding an increasing use in metallurgy and provision is made for 
four grades in A.S.T.M. Tentative Specification A 323-52. The range in chemical 
composition of these grades is shown in Table 36. 

Table 36 

Tentative Specification for Ferroboron, A.S.T.M. A 323-52 










Per cent. 

Per cent. 

Per cent. 

Per cent. 

Per cent. 

Grade A . 






Grade B . 






Grade C . 






Grade D . 






Ferroboron was being produced by three companies in the United States in 1958, 
two using electric furnace methods and one the alumino thermic process. The alloy 
produced, which averaged 6-3 per cent, boron, was used in making 219,250 short 
tons of alloy steel ingots. 

A boron-aluminium alloy containing 20 per cent, of boron is available commer- 
cially and is used as a means of introducing boron into other alloys and in steel. 

Calcium boride is being increasingly used in metallurgy, chiefly as a deoxidizer 
of copper and some non-ferrous alloys, particularly silicon bronze. It also serves 
as a convenient source of boron for the preparation of metallic borides, boron 
alloys and metallic boron. It can be prepared by the electrolysis of a fused bath 
containing lime, boric oxide and calcium chloride. 

Borax Consolidated Ltd., London, have available in commercial quantities 
a wide variety of metallic borides in both technical and chemically pure grades. 
These include the mono- and diborides of chromium, niobium, molybdenum, 
tantalum, and tungsten, and the diborides of titanium, vanadium and zirconium. 
Most of the technical grades have a fairly high degree of purity and contain 
0-1-0-2 per cent, iron and a maximum of 0-1 per cent, carbon. 



Rocket Fuels. Boron hydrides have received attention in recent years owing to 
their experimental use in rocket fuels, particularly diborane B 2 H 6 . Their high 
calorific value and the low atomic weights of their products of combustion make the 
boranes amongst the best of rocket fuels in terms of thrust per unit weight of fuel. 

One process described for making boron fuels is reported to be reduction of either 
boron trichloride or trifluoride with lithium hydride or sodium borohydride, to 
produce diborane, which is later converted to penta- or decaborane and then alky- 
lated. Sodium borohydride is made by Metal Hydrides Inc. of Beverley, Mass., 
U.S.A. by reacting sodium hydroxide with methyl borate in an inert mineral oil. 

Sodium borohydride, NaBBU, is a white crystalline solid which can be used as a 
source of hydrogen, one g. liberates 2-37 1. as compared with 11 1. for calcium 
hydride and 2-8 1. for lithium hydride. It is useful for the preparation of metallic 
borohydrides and is a powerful reducing agent for organic compounds. 

Three boron compounds, sodium borohydride, boron trichloride and boron 
trifluoride, are stated to be intermediates in the production of some high-energy 
fuels. Such fuels have been produced for the U.S. Navy by the Callery Chemical 
Co.'s plant at Muskogee, Oklahoma, and also by the Olin Mathieson Chemical 
Corporation at Model City, New York. 

Other Uses. Borax is used as a solvent for the casein employed in the manufacture 
of glazed papers and playing cards; in adhesives, calcamines, laundry starch, for 
pest control in citrus fruits and lumber, and for coating steel wire prior to dry 

Both boric acid and ammonium pentaborate are constituents of the electrolyte 
used in condensers for radio equipment. Potassium pentaborate is employed in 
some soldering fluxes. In recent years the importance of boron as a trace element 
in soils has been recognized and borax is now added to many commercial fertilizer 
mixtures. Borax is used as an emulsifying agent in the preparation of face creams and 
cosmetics having a wax base. Boric acid and borax are used in many other pharma- 
ceutical and toilet preparations. 

Boron trichloride, as offered by the American Potash and Chemical Corpora- 
tion, has the following percentage composition: boron trichloride, 99-5; free 
chlorine, 01; silicon, 0001; sulphur, as SCI, 003 (max.); carbon, as COCl 2 01 
(max.). It is a clear fuming liquid, melting at -107° C, boiling at 12-4° C. (at 
760 mm.) and has a density of 1 -43 at 0° C. Boron trichloride, which is an extremely 
reactive substance, can be used for the preparation of elemental boron, in degassing 
and refining aluminium, and for extinguishing fires in certain magnesium heat treat 
furnaces. It is usually transported in steel cylinders. 

Boron tribromide, as offered by the American Potash and Chemical Corpora- 
tion, is of about 99-5 per cent, purity. It is a clear amber, fuming liquid, melting 
at -46°C, boiling at 90-5°C. (at 760 mm.), and has a specific gravity of 2-62 at 
25°C. It reacts vigorously with water to form boric acid and hydrobromic acid, and 
with many organic compounds, such as alcohols and amines. It has been proposed 
for use as a catalyst, for the preparation of elemental boron. Trimethoxy boroxine 
is used as a fire extinguisher for metal fires. 

Sodium pentaborate, Na 2 B 10 O 16 .10H 2 O, which contains 58 per cent, of B2O3, 

M.OA.I— e 97 


is used as a weed killer, for fruit washing, as an ingredient in cotton defoliant and in 
fireproofing compositions where a high solubility of B2O3 is desired. It is also used 
as a food preservative in countries which permit the use of borates for this purpose. 
A number of borate esters are available for use as intermediates in the preparation 
of fuel additives, high temperature polymers and neutron absorbents. 


" The Industrial Development of Searles Lake Brines." By J. E. Teeple. Amer. Chem. Soc. Monogr. 

Ser. No. 49, New York, 1929, 182 pp. 
" Boron and Its Compounds." By R. M. Santmyers. U.S. Bur. Mines, Inform. Circ. No. 6499, 

1931,37 pp. 
" Borates." Anon. Min. Indus, of the Br. Empire and Foreign Countries. Imperial Institute, Lond., 

2nd Ed., 1933, 44 pp., including bibliography. 
" Production of Calcium Borate from Colemanite by Carbonic Acid Leach." By R. G. Knicker- 
bocker, A. L. Fox and L. A. Yerkes. U.S. Bur. Mines, Rep. Invest. No. 3525, 1940, 18 pp. 
" An Electrolytic Method for the Production of Calcium Boride." By J. Koster, R. G. Knicker- 
bocker, and A. L. Fox. U.S. Bur. Mines, Rep. Invest. No. 3500, 1940, 21 pp. 
" Borax and Boric Acid in Salt Glazing." By H. G. Schurecht and K. T. Wood. Ceram. Exp. 

Stat. N. Y. State Coll. of Ceramics, Bull. No. 2, 1942, 48 pp. 
" Technology of Borax Production as Practised by the Pacific Coast Borax Co." By G. A. 

Connell. Amer. Chem. Soc. (Pittsburg meeting), 1943. 
" Ceramic Glazes." By F. Singer. Borax Consolidated Ltd., London. 95 pp., including biblio- 
" Deposition of Pure Boron. I. Static Method of Preparation of Boron Coatings." By H. I. 

Schlesinger, G. W. Schaeffer and G. D. Barbaras. U.S. Atomic Energy Comm., May, 1944. 

M.O.D.C— 1338. 20 pp. 
" Some Possibilities for Rocket Propellants." (Boron Hydride.) By A. S. Leonard. /. Amer. 

Rocket Soc, 1946, No. 68. 
" Boron in Iron and Steel." By R. S. Dean and B. Silkes. U.S. Bur. Mines Inform. Circ. No. 7363, 

1946, 56 pp., including bibliography. 
" Boron Compounds." Encyclopedia of Chemical Technology. Ed. by R. E. Kirk and D. F. 

Othmer. New York, 1948, Vol. 2, 35 pp. 
"The Rarer Metals." By J. de Ment, H. C. Dake and E. R. Roberts. Lond., 1949 (Boron; pp. 

" Boron Trifluoride and its Derivatives." By H. S. Booth and D. R. Martin. New York and 

London, 1949, 315 pp. 
" The Use of Boron in Steel Production." By F. J. Robbins and J. J. Lawless. Metal Prog., 1950, 

57, 819 
" Nonmetallic Minerals." By R. B. Ladoo and W. M. Myers. New York, 1951 (Borax and Borates, 

pp. 107-17, including bibliography). 
" Boron." By H. S. Cooper in " Rare Metals Handbook," Ed. by C. A. Hampel, 1954, 657 pp. 

(Boron pp. 71-86.) 
" The Chemistry of Borates." Part 1, by P. H. Kemp. Borax Consolidated Ltd., London, 1956, 

90 pp. 
" Boron, Calcium, Columbium and Zirconium in Iron and Steel." By R. A. Grange et al., New 

York, 1957, 547 pp. 
" Borax and Boron Compounds." By R. M. Curts. Bull. Amer. Ceram. Soc, 1957, 36 (June 15). 
" Neuere Entwicklungslinien der Borochemie." By Von Egon Wiberg. " Mineral Chemistry," 

16th Int. Cong. Pure & App. Chem., 1957, Lond., 1958, pp. 417^146. 
" The Cubic Form of Boron Nitride." By R. H. Wentorf Jr. Ibid., pp. 535-7. 
" Elemental Boron." Technical Data Sheet 1-B, Borax Consolidated Ltd., London, 1958, 10 pp. 
" Sodium Borohydride," Technical Bulletin 502H, Metal Hydrides Inc., Beverly, Mass., U.S.A., 

1958, 5 pp. 
"Process for Production of Boron Carbide." By E. G. Gray, U.S. Patent 2,834,651, 1958. 
" Sodium Perborate and Sodium Percarbonate." Laporte Chemicals Ltd., London, 18 pp. 
" Metallic Borides." Technical Data Sheets 3-B, 4-B, Borax Consolidated Ltd., London, 1958, 

3 PP. 
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Met. Petrol. Eng., 3rd Ed., 1960, 103-118 
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7 pp. 
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Smelting Corporation, London. 



"Boron Trichloride." Product Information Sheet DB-25, American Potash and Chemical 

Corporation, Los Angeles, 4 pp. 
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American Society for Testing Materials 
A.S.T.M. Standards, 1958: 

Ferroboron. A.323-52. 

Borax for washing, cleansing and scouring purposes. D.929-50T. 
17.5. Ordnance Corps, Picatinny Arsenal, New Jersey: 

Boron, Amorphous Powder PA-PD-451 of 12 Nov., 1954. 


Bromine is a constituent of certain comparatively rare minerals, such as bromyrite 
(bromide of silver) and embolite (chlorbromide of silver), but the world's supplies 
of elemental bromine are derived from three main sources; (1) sea water, (2) brines, 
(3) as a by-product in the recovery of potassium salts from bedded saline deposits. 
Bromine is the only non-metallic element that is liquid under normal conditions 
of temperature and pressure. It never occurs uncombined in nature. 

World Production 

The world's recorded production of bromine, which in 1938 amounted to about 
17,800 long tons, rose very rapidly during World War II owing to the demands for 
its use in anti-knock compounds for aviation petrol. Thus the United States pro- 
duction rose from 14,900 long tons to a wartime peak of 45,400 long tons in 1944. 
Recovery from sea-water was started at this time in Great Britain. In 1958 the 
world's recorded production of bromine totalled about 84,000 long tons, obtained 
principally from the United States (over 94 per cent.), France, Japan, Israel, Italy, 
India, Spain and Federal Germany, as shown in Table 37. 

Table 37 

World Production of Bromine* (lb. avdp.) 

Producing Country 







France (6) 














Spain . 







United States (6, c) . 












1, 075.000(d) 


Japan . 














Bromine is also produced in the United Kingdom (from sea-water), the U.S.S.R. and in Germany. 
* Statistics supplied by the Statistical Section, Mineral Resources Division, Overseas Geological Surveys, 

(a) Information not available. 

(b) Sales. 


Includes bromine content of compounds. 




Extraction of Bromine 

United States. Most of the bromine recovered is obtained from raw sea-water, 
which contains about 67 parts per million of the element. The largest producer 
is the Ethyl Dow Chemical Co., which operates at Freeport, Texas. Next in im- 
portance is the Dow Chemical Corporation of Midland, Michigan, which, with four 
other companies, obtains bromine from well brines. 

The recovery of bromine from sea-water bitterns is accomplished by one of 
three processes: (a) a batch process using sulphuric acid and an oxidizing agent, 
such as sodium chlorate or manganese dioxide; (b) a continuous process using 
chlorine gas; or (c) a continuous process in which the bromine is liberated by 
electrolytic means. 

The American Potash and Chemical Corporation recovers bromine, amongst 
many other products, from Searles Lake, California, and the Westvaco Chlorine 
Products Corporation treats sea-water bitterns in California. These bitterns may 
contain the equivalent of from 014 to 0-20 per cent, of sodium bromide. 

In the process for extracting bromine from raw sea-water, the fish and debris 
are removed by screening, the water is acidulated with sulphuric acid and, after 
being treated with chlorine, is pumped to the top of the " blowing out " towers. 
Here the liberated bromine is blown out of the liquid by a counter current of air and 
passed to towers, where it is absorbed in a solution of sodium carbonate. The 
resultant solution of sodium bromide and bromate is next treated with acid and the 
liberated bromine collected in columns, from whence most of it goes to react with 
gaseous ethylene to form ethylene dibromide. 

In the United States the above " alkaline " process has been superseded by the 
so-called " acid " process, in which the bromine-laden air on leaving the towers is 
mixed with gaseous sulphur dioxide, which results in the formation of a mixture of 
hydrobromic and sulphuric acids which condenses and is separated from the air- 
stream in large spray catchers or absorbers. The condensed acid mixture is then 
chlorinated and the freed bromine is recovered by steam distillation. 

Germany. Bromine is obtained from the bitterns remaining after the extraction of 
potassium compounds from salts mined in the Stassfurt area. The bitterns treated 
contain magnesium bromide equivalent to 0-2-0-4 per cent, bromine, as compared 
with 0067 per cent, in sea-water. Before World War II, of the fifty companies 
working the Stassfurt deposits, only twelve had bromine recovery plants. At that 
time, Germany marketed the following three grades of bromine: (1) crude, contain- 
ing 2-5 per cent, chlorine; (2) refined, carrying up to 0-3 per cent, chlorine; (3) 
chemically pure, free from chlorine but containing a trace of organic matter. 

France. Important quantities of bromine are recovered from the potash deposits 
of Alsace, the sales in 1958 being about 1,585 long tons. 

A plant to separate bromine from sea-water by the Dow process was built at 
Port-du-Bouc on the Mediterranean coast during World War II and operates to 
supply French industry with the ethylene dibromide required. 

Israel. Bromine has been recovered from the liquors which remain after the 
extraction of potassium chloride from the waters of the Dead Sea, the bromine 
content of which varies from about 0-4 per cent, at the surface to 0-7 per cent, at 



about 500 feet depth. To meet war-time demands the output of bromine, which 
totalled 589 long tons in 1939 was stepped up to 792 long tons in 1942. In 1945, 
however, it had fallen to 293 long tons and it ceased in 1947 owing to unsettled 
conditions in Israel. The bromine, which had a purity of about 99-5 per cent, with 
chlorine not exceeding 0-3 per cent, and no organic matter, was used in Great 
Britain chiefly in the manufacture of methyl bromide and bromides of sodium, 
potassium, ammonium and calcium. It was not used, however, for the production of 
ethylene dibromide for anti-knock compounds. In 1 957, Israel recorded a production 
of about 640 long tons of bromine and compounds. The Dead Sea Bromine 
Company which operates at Sodom, uses mother-liquors containing about 
1 per cent, of magnesium bromide for the production of bromine and ethylene 

Great Britain. During World War II a plant was erected in Cornwall for the 
extraction of bromine from sea-water by the Ethyl-Dow alkaline process. Although 
the plant was installed as a wartime measure, it is now being worked on a com- 
mercial basis with an output of about 3,600 long tons per annum. A second plant 
in Anglesea, supplies the ethylene dibromide required by the tetraethyl lead plant 
at Ellesmere Port. 

The bromine recovered has a purity varying between 99-85 and 99-95 per cent., 
the only impurity being chlorine. 

Great Britain's home production of about 11,000 long tons is augmented by 
imports of bromine, which in 1958 amounted to 300 long tons. Great Britain is an 
exporter of bromine, ethylene dibromide and other bromides. 

India. Bromine is being recovered from bitterns by Tata Chemicals Ltd., at 
Mithapur, India, together with some magnesium chloride and magnesium sulphate. 

The installed capacity for the production of bromine by Tata Chemicals Ltd., 
at the end of 1959, was about 50,000 lb. per month. This will be raised to 60/70,000 
lb. per month by 1961. Part of the present output is converted to bromides of 
sodium, potassium and ammonium by the producers. 

Union of South Africa. A new plant for the extraction of bromine and other 
chemicals from sea-water started production in 1949 in Jacob's Bay, four miles 
west of Saldana Bay, with a planned annual production of about 200 long tons of 


The quantities of bromine and bromides sold by producers in the United States 
in recent years, as shown in Table 37A, afford a useful indication of the amounts 
taken by the various industries in that country {see p. 102). 

The principal use for bromine is in the production of ethylene dibromide 
(C2H4Br 2 ), which in turn is employed in equimolecular proportions with tetra-ethyl 
lead (Pb(C2H 5 )4) in the manufacture of anti-knock or ethyl fluid for treating petrol 
for aviation purposes. For automobile petrol, about 50 per cent, of the ethylene 
dibromide is replaced by ethylene dichloride. 

Bromine is also used to a lesser extent for the production of bromides of sodium, 
potassium, ammonium and calcium, which are used in pharmacy and photography. 



Table 37A 

Bromine and Bromides sold by United States Producers* 
Bromine Content {lb. avdp.) 

1957 1958 

Elemental bromine .... 

Potassium bromide 

Other uses, including ethylene dibromide, sodium bromide \ 
and ammonium bromide ..... J 



I 161,993 




*From Minerals Yearbook, U.S. Bur. Mines, 1958. 

Hydrogen bromide and its aqueous solution, hydrobromic acid, rank among the 
more important brominating agents. Hydrobromic acid can be prepared of any 
desired strength up to about 70 per cent., but it is generally supplied commercially 
in strengths of 30, 40, 48 or 62 per cent, hydrogen bromide. The acid can be made by 
the reduction of bromine in water by SO2, H 2 S or free sulphur, and the process can 
be operated either as a batch or continuously. A process using sulphur is described 
in British Patent 551,789 of March 10, 1943. 

Zinc bromide marketed in solid form or as an 80 per cent, solution is used in 
rayon finishing, as a catalyst, in certain non-inflammable nitrocellulose compounds 
and as a radiation shielding device (see p. 730). A comprehensive account of the 
preparation and properties of a large number of both organic and inorganic bromine 
compounds is given in " Bromine, Its Properties and Uses," published by the 
Michigan Chemical Corporation, of St. Louis, Michigan, U.S.A. 

Bromine is also a constituent of certain " tear " gases, and of methyl bromide 
which is being used increasingly as a fire extinguisher, for the extermination of insect 
and rodent pests, and for fumigation. Methyl bromide, CH 3 Br, has been extensively 
used as a space fumigant for the control of insects in warehouses and storage plants. 
It is a colourless gas at ordinary temperatures, which liquifies under pressure. Its 
boiling point is -4-3°C. and the specific gravity of liquid methyl bromide is 
1 -732 at 0° C. At one time, a salt consisting of bromide and bromate of sodium, and 
known as " mining salt," was used for extracting gold from telluride ores. 

A series of brominated compounds for flameproofing, with self-extinguishing 
characteristics, have been introduced by the Michigan Chemical Corporation of St. 
Louis, U.S. A. The products are stated to be tetrabromo&wphenol A; tetrabro- 
mothallic anhydride; tris (2-bromo-ethyl) phosphate; and pentabromophenol. 
Chlorobromo methane is also used as a non-corrosive fire-extinguishing fluid. 

Bromine compounds, such as ethylene dibromide, methyl bromide and chloro- 
bromopropene are used as soil fumigants to control nematodes. 

Potassium bromate is added to soya and high protein wheat flour to improve 
their baking characteristics and is an ingredient in certain yeast foods. According to 
standards formulated in May, 1952, by the United States Federal Security Agency, 
Food and Drug Administration, potassium bromate may be an optional ingredient 



in bread to the extent of not more than 00075 parts for each 100 parts by weight of 
flour used. 

A well-known British maker of bromides for pharmaceutical purposes requires 
bromine containing not more than 0-2 per cent, chlorine; arsenic not over 00001 
per cent. ; non-volatile matter, 01 per cent. Sulphur compounds must be absent. 


" Bromine." Anon. Reps, on Min. Indus, of the Br. Empire and Foreign Countries. Imperial 

Institute, London, 1928, 19 pp., including bibliography. 
" Bromine and Iodine." By P. M. Tyler and A. B. Clinton. U.S. Bur. Mines, Inform. Circ. No. 

6387, 1930, 26 pp. including bibliography. 
" La Fabrication de Brome en France." By M. Koltenbach. Chimie et Industrie, 1931, 25, 543-55. 
" Commercial Extraction of Bromine from Sea Water." By L. C. Stewart. Industr. Engng. Chem., 

1934, 26, 361-69; and Trans. Canad. Inst. Min. Met., 1938, 41, 443-47. 
" Bromine as a Chemical Raw Material." By L. C. Stewart. Chem. Industries (N.Y.), 1937, 41, 

" Minerals from the Sea." By E. F. Armstrong and L. M. Miall. Leicester, 1946, 164 pp. (Brom- 
ine, pp. 72-85). 
" Minerals from the Sea." By C. M. Shigley. /. Metals, 1951 (Jan.), 25-9. (Describes processes for 

extraction of bromine.) 
" Bromine." " Encyclopedia of Chemical Technology." Ed. by R. E. Kirk and D. F. Othmer. New 

York, 1948, Vol. 2, 629-59, including bibliography. 
" By-products of Salt Manufacture from Sea-water and Sub-soil Brines." By G. V. Dange, J. P. 

Jassawala and M. Prasad. /. Scl. Ind. Res. (India), 1952, 2 (No. 3), 87-90. 
" Bromine, Its Properties and Uses." Michigan Chemical Corporation, 1958, 62 pp. (incl. 506 

biblio. refs.) 
" Bromine." By Paul Pascal. Nouveau Traite de Chimie Mineral. Ed. by P. Pascal. Vol. xvi, 1960, 

" Bromine." By R. N. Shreke. *' The Chemical Process Industries." New York, pp. 418-421. 
" Bromine." By H. E. Stipp in " Mineral Facts and Problems." U.S. Bur. Mines Bull. 585, 1960, 

6 pp. 
" Bromine." U.S. Bur. Mines. Minerals Yearbook (Annual). 


The only noteworthy mineral in which cadmium occurs as an essential constituent 
is Greenockite, a sulphide of the metal. This mineral, however, is rare and is not 
found in commercial quantities. 

The chief sources of supply are the flue dusts produced during the smelting of 
zinc concentrates, smaller amounts being obtained from dusts resulting from the 
roasting of copper and lead-zinc ores, and the high cadmium precipitates obtained 
in purifying zinc electrolyte at electrolytic zinc plants. The cadmium content of 
zinc ore concentrates varies with ore from different localities, and with the processes 

Zinc concentrates from some mines in Peru are stated to average nearly 1 -4 per 
cent, but most Peruvian zinc ore carries about 0-3 per cent, cadmium. North 
American zinc ores are recorded to contain between 0-10 and 0-6 per cent., but 
Australian are mainly between 01 and 0-2 per cent. Ores from South- West Africa 
are relatively rich in cadmium, zinc concentrates carrying about 1 -5 per cent., whilst 
lead-copper concentrates contain about 0-5 per cent. This latter is rather excep- 
tional as lead ores are usually low in cadmium, often between 0-02 and 05 per cent. 



It has been stated that the recovery of cadmium per ton of recoverable zinc 
averages about 18 lb. in Mexico, 8-8 lb. in Western Canada and Peru, and about 
4-4 lb. in Australia. It has been estimated that from 60 to 75 per cent, of the 
cadmium present in the zinc ore concentrates is recovered. 

World Production 

The world's annual production of cadmium, which amounted to about 4,500 
long tons in 1938, rose to a peak of 6,000 long tons in 1943. Since that time produc- 
tion has increased and in 1957 totalled about 9,375 long tons. 

The largest producer for some years past has been the United States, which 
accounts for over 50 per cent, of the total and in most years has an exportable 

The second largest is South-West Africa, whose production is in the form of 
copper-lead-zinc concentrates, which are exported for treatment. Third comes 
Canada, which produces cadmium principally from the lead-zinc ore mined in 
British Columbia, both as metal and in concentrates. Next comes Mexico, whose 
product is exported mostly in the form of flue dust. Other large producing countries 
in order of output are: Belgium, U.S.S.R., Belgian Congo, Australia, Japan, 
Federal Germany, Poland, Italy, France, Norway, United Kingdom, Peru and 
Northern Rhodesia. The largest consumer of cadmium is the United States, which in 
1958 used 3,660 tons of cadmium metal. 

In 1957, Great Britain extracted about 102 long tons of cadmium, chiefly from 
imported ores. In 1958 imports of metal for consumption were 823 long tons of 
which 308 long tons came from Canada, 212 long tons from the United States, and 
177 long tons from Australia. 

In addition to the new cadmium recovered from ores, important quantities of 
secondary cadmium metal, or its compounds, are obtained from the treatment of 
scrap. The country having the largest output of secondary cadmium is the United 
States, which in 1955 recovered 285,800 lb. of metal. Figures for 1956 and 1957 were 
not published. 

Extraction of Cadmium 

The starting point for the recovery of cadmium is usually the smelter fume and 
dusts which are collected in the baghouse when cadmium-bearing ores are roasted 
or their metals distilled. As cadmium is more volatile than zinc and its oxide is also 
more easily reduced, much of the cadmium can be removed before the zinc is 
volatilized. The efficiency of cadmium recovery has increased considerably in recent 
years. Thus, in the United States the recovery from zinc ores in the years 1941^5 
averaged 6 lb. per ton of recoverable zinc, and this had been raised to 8-6 lb. by 

Several processes are in use for the extraction of cadmium from fume or flue 
dusts, the technique of these methods depending on the nature of the other metals 
present. Most processes, however, involve chemical and metallurgical treatment too 



varied and detailed to be described here, but a full account will be found in 
" Cadmium " by N. F. Budgen. 

Some physical properties of cadmium are as follows: 

Atomic number, 48 

Atomic weight, 112-4 

Crystal form Hexagonal pyramids and prisms 

Melting point, 321° C. 

Boiling point, 767° C. 

Density (at 20° C), 8-65 g./cc. 

Specific heat (at 321-600° C), 0-0632 (g. cal./g.) 

Thermal neutron absorption cross-section 2,500 barns/atom 

Coefficient of linear expansion at 250° C, 29-8 x 10- 6 cm/°C. 

Natural Isotopes (abundance) 


. 1 -4 per cent 


• io „ 


.12-8 „ 


.13-0 „ 


.24-2 „ 






• 7-3 


Before 1939 the chief uses for cadmium were as an alloy with copper for over- 
head electric conductors, which were required to have a high resistance to abrasion; 
in bearing-metal alloys; in certain types of electrical storage batteries; and as a 
basis for pigments, such as cadmium lithopone, cadmium yellow, etc. During 
World War II the use of cadmium for electroplating increased considerably both in 

Table 38 

United Kingdom Consumption of Cadmium.* 

Long tons 





Plating anodes 
Plating salts . 
Cadmium copper 
Other alloys 
Batteries: Alkaline 

Solder . 








. 79-00 




4- 10 




Total consumption 





* From " Bulletin, British Bureau of Non-ferrous Metal Statistics," Birmingham, 
England, 1959. 



this country and in the United States and now accounts for possibly 80 per cent, of 
the consumption in the latter country. 

The consumption in Great Britain in 1955 to 1958 was distributed as shown in 
Table 38. 

The consumption of cadmium in the United States in 1955-6 is shown in Table 
39; statistics for later years are not available. 

Table 39 

Cadmium consumption in the U.S.A. by Uses, per cent, of total 



Pigments and chemicals 
Low melting alloys 
Brazing alloys 
Other metals and alloys 

Bearing alloys 
Other uses . 



Total consumption (short tons) 



The degree of purity of cadmium metal required by consumers varies with the 
purpose for which it is to be used. Cadmium containing thallium exceeding 005 
per cent, is not generally acceptable to electroplaters, but bearing metal manu- 
facturers will often accept metal containing up to 05 per cent, thallium. The maxi- 
mum percentage of lead tolerated by platers is 05, whilst bearing metal makers 
place the limit at 0-02 per cent. Some specifications from American sources are 
summarized in Table 40. 

Table 40 

U.S. Specifications for Metallic Cadmium 

U.S. Bureau 

of Federal 



Bearing Manufacturers 
(a) (*) 

Cadmium, min. 

Copper, max. . 

Iron, max. 

Lead + silver + tin, max. . 

Zinc, max. 

Antimony + arsenic + thallium, 

max. .... 
Lead, max. 
Bismuth, max. . 
Antimony, max. 
Tin, max. .... 
Silver, max. 
Nickel, max. 

Per cent. 


Per cent. 


Per cent. 





Per cent. 









The U.S. National Stockpile Specification P-8 of March 27th, 1952, for the 
purchase of metallic cadmium in the form of ingot, slab, ball or stick, requires the 
product to contain a minimum of 99 -9 per cent, of the metal, with a maximum limit 
of 05 per cent, for lead, silver and tin, and 005 per cent, for arsenic, antimony 
and thallium. 

The average percentage composition of the metallic cadmium produced by the 
Electrolytic Zinc Company at Risdon, Tasmania, is cadmium, 99-959; copper, 
0009; zinc, 0263; lead, 0136; iron, 0002. 

Alloys. Cadmium is often used as the principal constituent of bearing alloys used 
in aero-engines. One such alloy contains 98-65 per cent, of cadmium and 1-35 per 
cent, of nickel. Another type contains 0-2-2-5 per cent, of silver and 0-25-2 per cent, 
of copper in place of the nickel. 

Cadmium is also a constituent of certain so-called " fusible alloys " which have 
low melting points (see Bismuth, p. 87). 

Copper containing 0-7 to 1 per cent, of cadmium is ductile and finds wide use 
in telegraph, telephone and power transmission wires on account of its high tensile 
strength, good conductance and resistance to wear. 

Nuclear Energy. Cadmium metal readily absorbs thermal neutrons and for this 
reason has been used as a shielding material, usually in conjunction with lead. The 
absorption of neutrons causes the cadmium to emit gamma rays which, in turn, are 
stopped by the lead. Some nuclear reactors erected in the United States employ 
cadmium in the control rods, a layer of the metal 004 to 008 inches thick being 
sprayed on to sheet aluminium and the layer protected by a coating of aluminium 
sprayed over it. 

Cadmium is also used as a protective lining material for vaults in which uranium- 
bearing fuel elements are stored. 

Solar Energy. A solar energy generator using cadmium sulphide, processed into 
crystal form, for converting sunlight into electrical energy was developed by the 
U.S. Air Force in 1954. It was stated that a wafer-thin slab 4 ft. by 15 ft. would 
supply current enough to meet the needs of an average home. Attached to opposite 
sides of the crystal are electrodes, one of silver serving as the anode and another of 
indium for the cathode, the circuit being formed by a wire from the silver to the 
motor or battery and back to the indium, thus completing the circuit. Cadmium 
sulphide photocells are made by the British Thomson Houston Company of Rugby. 

Cadmium Plating. A protective coating of cadmium can be applied to many 
metals by spraying or hot dipping, but electrodeposition is the more general method. 
Electrodeposited cadmium coatings are claimed to be superior to those of zinc for 
some purposes, as thinner coatings give equal protection under certain conditions, 
such as those involving exposure to alkali or salt water. Other advantages claimed are 
greater ease in soldering, less power required for deposition and the cadmium deposit 
retains its lustre longer. One important use is as a protective coating for small iron 
or steel articles, e.g. nuts, bolts, fasteners, automobile and aircraft parts and radio 
equipment. Electro-deposited cadmium as a protective coating for steel, iron and, to 
a less extent, copper alloys, constitutes the largest use of the metal. The deposit, 
which has a high lustre, is harder than silver and as white as tin, and is not tarnished 



by sulphurous gases in the atmosphere. Household articles are often plated with a 
deposit of cadmium containing 7-5 per cent, of silver. Plating is usually done with 
cyanide solutions. 

British Standard Specification B.S. 2868 : 1957 for cadmium anodes and cad- 
mium oxide for electroplating requires that the anodes shall contain not less than 
99-95 per cent, of cadmium. The cadmium content cannot be determined by chemi- 
cal methods, but shall be obtained by difference, using spectrographic means for 
determining the impurities, which shall not exceed the following: Total impurities, 
05 per cent.; antimony plus arsenic plus thallium, 01 per cent. Cadmium oxide 
shall be in the form of brown powder and shall conform to the formula CdO. It 
shall contain not less than 99 per cent. CdO. Loss on ignition shall not be more than 
0-5 per cent., when determined by heating for two hours in an open muffle at 800° C. 
The insoluble matter, when determined by the prescribed methods, shall not be more 
than 01 per cent. The following impurities, if present, shall not exceed the limits 
stated (when determined spectrographically) : total metals, 05 per cent.; antimony 
plus arsenic plus thallium, 01 per cent. 

Cadmium is sometimes electro-deposited on steel as a preventative of corrosion. 
A.S.T.M. Specification No. A 165-55 for electro-deposited coatings of cadmium on 
steel provides for three grades differing in minimum thickness, i.e. 3-8/*, 7-6/t and 

Storage Batteries. Nickel-cadmium alkaline electrical storage batteries are widely 
used in Europe for industrial and railroad units, but were not manufactured in the 
United States until 1946. 

The characteristics of such batteries are that they do not suffer from being 
entirely discharged and left in that condition; they will withstand a rapid rate of 
discharge without deterioration of the plates, and they can be left fully charged for 
long periods without attention. For these reasons they are suitable for use in miners' 
lamps, electrical storage batteries in railway trains and for aircraft use. Some details 
concerning construction of these cells are given under " Nickel " (see p. 412). Each 
standard size auto battery requires about 7 lb. of cadmium, but if sintered plates 
are used only about 1 -4 lb. is needed. 

Capital Airlines Ltd. (U.S.A.) announced in 1958 that their Vickers Viscount 
aircraft were supplied with two 24-volt, 28 ampere-hours nickel-cadmium batteries 
in place of the lead-acid batteries previously employed. This replacement was stated 
to have reduced maintenance costs by 80 or 90 per cent. 

Research work was in progress in 1958 at the Wright Air Development Center, 
Ohio, on a cadmium sulphide electric generator which developed 50 milliwatts at 
8 volts when exposed to direct sunlight. 

Cadmium Compounds. Chemical manufacturers employing cadmium metal as 
the starting point for producing the oxide and the salts prefer a high purity metal. 
One specification is Cd 99.95; Pb, not exceeding 0014; Fe, 0007; and Zn, 001 per 
cent. Another user specifies a metal with the following limits for impurities: Pb, 
005 per cent., Al and Fe, traces; As, 5 p.p.m., and alkalis, nil. 

Cadmium Pigments. In recent years there has been an increasing demand for 
certain cadmium compounds for use as high-grade pigments. Cadmium pigments, 



particularly cadmium lithopone or " Cadmophone," are available in a full range of 
yellow, orange and red colours, which are unaffected by temperatures up to 500° C. 
The colours are fast to light, have no tendency to bleed in oil, organic solvents, 
spirits or water, and do not migrate when compounded in rubber or synthetic resins. 
They are resistant to soda, lime, ammonia and to dilute solutions of most acids. 
The yellow colours are based on cadmium sulphide, whilst the red, maroon and 
orange colours contain varying amounts of cadmium sulpho-selenide. 

In addition to their use in paints, enamels and lacquers, cadmium pigments are 
employed in the printing ink trade, especially for lithographic and offset work. 

In the ceramic industry, cadmium pigments are used for red and yellow shades 
in fired ware and also in vitreous enamels. Yellows for the latter are sometimes 
specified as being basic cadmium sulphide, that is, containing small amounts of 
oxide, hydroxide or carbonate. 

In glass manufacture, the basic cadmium sulphide described above may be used 
in conjunction with selenium, either as a decolorizer or to vary the tint of yellow 
through orange to ruby, as may be desired. Cadmium pigments, such as the sulpho- 
selenide, are sometimes used in special cases to produce opaque coloured glasses in 
decorated glassware. Transparent orange or red colours are, however, produced by 
mixing basic cadmium sulphide with appropriate amounts of selenium and adding to 
the glass melt, thus making the desired shade of sulpho-selenide direct during the 
manufacture of the glass, with the result that the pigment is dispersed through the 
melt in a finely divided state, so as to appear quite transparent. Traffic signals and 
ruby car lenses are made in this way. 

Cadmium sulphide-carbonate, which contains about 45 per cent, of cadmium 
sulphide (CdS) and 55 per cent, of cadmium carbonate (CdCOs) is chiefly used by 
ceramic colour makers to produce other cadmium pigments. 

Other Uses. Cadmium oxide, hydrate and chloride are used in electroplating; 
cadmium bromide, chloride and iodide in special photographic films, and cadmium 
salicylate as an external antiseptic in medicine. 

Cadmium Poisoning 

Inhalation of minute amounts of cadmium dust or fumes may cause throat 
irritation, headaches and vomiting, whilst exposure to larger amounts may cause 
lung trouble and even death. Inhalation of fatal quantities may occur without 
warning discomfort. According to the Canadian Industrial Health Bulletin, danger 
from cadmium poisoning may result when dust or fumes are produced from the 
grinding, burning or welding of cadmium-plated metals, cadmium alloys and 
metals covered with cadmium-bearing paint. 


" The Metallurgy of Zinc and Cadmium." By H. O. Hofman. New York, 1922 (Cadmium, pp. 

" Cadmium, Its Metallurgy, Properties and Uses." By N. F. Budgen. London, 1924, 239 pp. 
" Cadmium." Anon. Min. Indus. Br. Empire and Foreign Countries, Imperial Institute, London, 

1929, 23 pp., including bibliography. 
" Cadmium (Metallurgy)." By W. R. Ingalls. Trans. Amer. Inst. Min. Met. Eng. (" Reduction and 

Refining of Non-ferrous Metals "), New York, 1944, 159, 467-70. 



" Cadmium-Nickel Alkaline Battery." Nat. Res. Council Canada, Rep. No. E.R.B. 172, 1947, 

23 pp. 
" Nickel-Cadmium Storage Batteries in Germany." By P. E. Plehn. F.I.A.T. Final Rep. No. 800, 

1947,23 pp. 
" Bunker Hill Plant Recovers Metallic Cadmium from Zinc." By J. B. Hutte. Engne. Min. /., 

1946, 147 (No. 4), 82-85. 
" Cadmium Recovery Practice in Lead Smelting." By P. C. Feddersen and H. E. Lee. /. Metals, 

1949, 1 (Feb.), 110-17. 
" Recovery of Cadmium from Cadmium-Copper Precipitation at Risdon, Tasmania." By G. H. 

Anderson. /. Metals, 1949, 1 (Feb.), 205-10. 
" Cadmium Recovery Practice at Donora." By G. T. Smith and R. C. Meyer. J. Metals, 1949, 1 

(Feb.), 360-63. 
" Primary Batteries." By G. W. Vinal. Lond., 1950 (Cadmium, pp. 169-72). 
" Cadmium Pigments." By P. J. Curtis and R. B. Wright. /. Oil and Col. Chem. Asscn., 1954, 37, 

Jan., 26-43. 
" The Use of Cadmium Pigments in Polyvinyl Chloride." Johnson, Matthey & Co., London, 

12 pp. 
" Cadmium." By F. G. McCucheon and J. R. Musgrave in " Rare Metals Handbook." Ed. by 

C. A. Hampel, New York, 1954, pp. 87-102. 
" Cadmium, A Materials Survey." By R. L. Mentch and A. M. Lansche. U.S. Bur. Mins, Inf., 

Circ. 7881, 1958, 43 pp. 
" Eagle-Picker and Harshaw Progress in Solar Energy." Amer. Metal Market, 1958, 65, No. 1, 

1 and 1959, 66, No. 2, 7. 
"The Radiochemistry of Cadmium." By J. R. Devoe. Nuclear Science Series Nas-Ns 3001, 

National Academy of Sciences, Washington, D.C., U.S.A., 1960, 57 pp. 
"Cadmium." By A. M. Lansche. "Mineral Facts and Problems." U.S. Bur. Mines Bull. 

585, 7 pp. 
" Cadmium." U.S. Bur. Mines. Minerals Yearbook (Annual). 


American Society for Testing Materials. 
A.S.T.M. Standards, 1958: 

Electrodeposited Coatings of Cadmium on Steel. A1 65-55. 
U.S. National Stockpile Specification: 

Cadmium, Ingot, Slab, Ball and Stick. P-8, March 27th, 1952. 

Caesium and Rubidium 

These two rare elements usually occur closely associated in nature and it is conven- 
ient to consider them together. 

A number of minerals, e.g. leucite, spodumene, triphylite, carnallite, mica and 
orthoclase, carry traces of rubidium. Lepidolite has been known to contain almost 3 
per cent, of rubidium oxide, Rb20, and 0-7 per cent, of caesium oxide, CsaO. For 
analyses of lepidolite (see Table 104). Beryl may carry about 3 per cent, of CS2O. 
Many samples of crude potash and the mother-liquor from the Stassfurt potassium 
works have been found to contain rubidium and caesium and, at one time, these were 
used as a source of the elements. Caesium has been recorded to occur in the carnal- 
lite found at Solikamsk in the U.S.S.R. 

The only caesium mineral which has been found in commercial quantity is 
noll^c.ite.. a hydrous caesium, sodium, aluminium silicate, to which the formula 
(CsNa)203.Al203.5Si02.H20 has been assigned. It is a colourless mineral having 
a specific gravity of 2-9 and a hardness of 6-5. It is brittle and has a conchoidal 
fracture. Analysis of the mineral produced from the Joost mine in the Karibib 



district of South- West Africa (the chief producer and also the world's richest source 
of rubidium) shows the following percentage composition: caesium oxide, 28-63; 
silica, 46; alumina, 17; rubidium oxide, 1-31 ; potash, 1; lithium oxide, 0-31; soda, 
2 09; water, 2-50. Pollucite is also obtained at Bikita in Southern Rhodesia. 

At one time pollucite was mined at Newry, in Maine, U.S.A., by the General 
Electric and Westinghouse Electric Companies, and was utilized in the production 
of filaments for a special type of radio valve. 


Both caesium and rubidium are recovered from the residual alkali solution 
remaining after the extraction of lithium from lepidolite, by heating with sulphuric 
acid, diluting with water and then concentrating the solution until caesium and 
rubidium alums crystallize out. The alums are then separated by virtue of their 
difference in solubility in water. Caesium and rubidium are obtained by dissolving 
the respective alums in water, precipitating by oxalic acid and igniting the oxalate to 
the carbonate, CsC03 or RbC03. The metals are obtained by mixing the respective 
carbonates with powdered magnesium and heating the mixture in hydrogen. 
Caesium chloride of 99 per cent, purity is available commercially, and may be used 
as a source of the metal. 

Rubidium and caesium have been recovered from the electrolytic residues at 
Solikamsk in the U.S.S.R. in the production of magnesium by the electrolysis of 
artificial carnallite. These residues contain about 0057 per cent, of mixed rubidium 
and caesium chlorides. The alkali chlorides in the residues are converted to sul- 
phates; the solution is slowly evaporated so as to crystallize out most of the sodium, 
potassium and calcium sulphates, and the rubidium and caesium are precipitated by 
adding silico-molybdic acid. The precipitate is treated to remove silica and molyb- 
denum, the caesium and rubidium being finally recovered as nitrates. 

Metallic caesium is silver white in colour, melts at 26-5° C, boils at 670° C, 
and has a specific gravity of 1 -85. Rubidium melts at 38° C, boils at 696° C, and has 
a specific gravity of 1 -522 at 15° C. Both metals oxidize rapidly in air and therefore 
have to be stored under paraffin. 


Caesium. The principal use for caesium is in the manufacture of photo-electric 
cells in which the cathode is a thin film of metallic caesium deposited on a specially 
prepared silver conductor, whilst the anode consists of an open wire framework, 
usually of nickel. 

Recently the American Potash and Chemical Corporation of Los Angeles have 
manufactured technical grades of several salts of rubidium and caesium, which are 
obtained as by-products from the extraction of lithium compounds from lepidolite 
obtained from the Bikita (a) deposit in Southern Rhodesia. In Great Britain the 
compounds are marketed by Borax and Chemicals Ltd., a subsidiary of the American 
firm. Typical analyses of caesium carbonate, sulphate, chloride and fluoride 
marketed, all of which have a minimum purity of 93 per cent., are shown in Table 41 . 



Table 41 

Commercial Caesium Salts 

Melting point 

Caesium Carbonate 


Na 2 C0 3 






Caesium Sulphate 

R.D2SO4 5 0% 
Na 2 S0 4 0-2% 
K2 SO4 01 % 
Carbonate 00% 


Caesium Chloride 

RbCl 60% 
NaCl 0-2% 
KC1 01% 

Carbonate 0-5% 


Caesium Fluoride 







Most of the production of caesium and its compounds in the U.S.A. in 1956 
was obtained by the American Potash and Chemical Corporation, using as raw 
material a mixed rubidium-caesium potassium carbonate (" Alkarb ") obtained 
by its subsidiary, San Antonio Chemicals Inc., Texas, as a by-product from the 
extraction of lithium hydroxide from lepidolite. " Alkarb " contains about 2 per 
cent, caesium carbonate and is used chiefly in the production of certain types of 
glass, ceramic glazes and enamels. 

The ease with which caesium loses its outer electron even under the action of 
light has made the metal and its alloys valuable in the manufacture of photo-cells. 
Numerous patents have been granted covering the use of caesium for electron- 
emission cathodes and photo-cathodes : examples of these are U.S. Patent 2,685,531 
(1954), and 2,668,778 (1954) both granted to the General Electric Company. 
Caesium bromide and iodide are used as window materials in some infra-red 
detectors. The high degree of transparency of certain caesium halide crystals makes 
them useful for the manufacture of prisms for infra-red spectrometers, and the 
addition of such halides to zinc sulphide increases the absorption of X-rays, accord- 
ing to U.S. Patent 2,651,584 (1953) granted to the Westinghouse Electric Corpora- 
tion. Caesium hydroxide has been suggested as a replacement for the electrolyte in 
alkaline storage batteries in order to improve their operation at low temperature. 

Radioactive Caesium- 137 is obtained as a fission product from waste at the 
Windscale works of the U.K. Atomic Energy Authority. Caesium-137 has a long 
half-life — about 30 years — and a hard enough gamma ray to be useful as a source of 
radiation and is finding increasing use for small radiographic units for medical use. 
The method of separation, which involves precipitation of caesium as the phospho- 
tungstate, is described by B. F. Warner in " Progress in Nuclear Energy " series 
3, Vol. II. Caesium-137 is also recovered at the Hanford plant of the General 
Electric Company at Rickland, Washington, and in the U.S.S.R. As a general rule 
the caesium is recovered from the phosphotungstate compound by anion exchange 
and is marketed as the sulphate. 

Caesium-137 for medical use is usually enclosed in small metallic capsules, each 
of which contains material having an activity of 1,000 curies, equivalent to about 
1,000 gm. of radium. 

Caesium-137 has been proposed for the ionic propulsion of space ships, which 



according to E. Stublinger would require over 51 tons of the metal for a one year 

Numerous methods for preparing caesium cathodes have been described in the 
patent literature. One of these consists of the electro-deposition of a layer of silver 
on a base of electrolytic copper: next comes a layer of silver oxide (Ag20), followed 
by one of caesium oxide (CS2O) and finally a layer of metallic caesium. Another 
form of cell employs a thin layer of a caesium-antimony alloy on a base of antimony. 

In addition to being sensitive to white light the caesium cell can also be activated 
so as to respond to red or ultra-violet light and so is useful for night signalling. 

Mixtures of metallic rubidium and caesium are sometimes used in radio valves. 

Rubidium. Technical rubidium compounds marketed by the American Potash 
and Chemical Corporation include the carbonate, sulphate, chloride and fluoride, 
the compositions of which are shown in Table 41a. 

Table 41A 

Commercial Rubidium Salts 

point °C. 


Rb 2 C0 3 95%min. 
K2CO3 3 0% 

Na 2 C0 3 1-5% 

CS2CO3 0-2% 

Chloride (CI) 0-2% 



Rb 2 S04 95%min 
K2SO4 2-5% 
N2SO4 01 % 
CS2SO4 01 % 
Carbonate 0-5% 



RbCl 95%min. 














Rubidium salts do not appear to have found extensive use in industry, but their 
employment has been suggested for many purposes. It is claimed that certain rubi- 
dium halides added to zinc sulphide screens increase the absorption of X-rays, this 
use is covered by U.S. Patent 2,651,584 (1953) granted to the Westinghouse Electric 
Corporation. It has also been suggested that rubidium compounds can be used in 
the manufacture of photo-luminescent materials. Rubidium phosphate, RbH^POi, 
has piezoelectric properties and methods for producing crystals of suitable com- 
position are described in U.S. Patent 2,680,720 (1954) granted to the Clevite 
Corporation. For the more efficient operation of alkaline storage batteries at low 
temperatures (-50° C.) it is recommended that all or part of the electrolyte be 
replaced by rubidium hydroxide, this use being covered by U.S. Patent 2,683,102 
(1954) granted to R. S. Coolidge. Certain rubidium compounds are toxic and 
care should be exercised in handling them. 

Rubidium iodide has some use for treating syphilis and goitre, and some other 
salts of the metal are used in microchemical work. 


" Caesium, Rubidium and Lithium." By R. M. Santmyers. U.S. Bur. Mines, Inform. Circ. No. 

6215, 1930, 17 pp. 
" Separation of Rubidium and Caesium from the Electrolytic Residues at Solikamsk by Means of 

Silico-Molybdic Acid." By B. E. A. Nititina and A. G. Kogan. Compt. rend. Acad. Set 

U.S.S.R., 1941, 30, 509-10. 



" Caesium and Its Application in Photo-Electric Cells." By A. G. Arend. Metallurgia, 1944, 30, 

(May), 7-8. 
" Fabrication des Cellules Photoelectriques." By J. Berthiller. Electricite, 1947, 31, 69-74. 
" The Rarer Metals." By J. de Ment, H. C. Dake and E. R. Roberts. Lond., 1949 (Rubidium and 

Caesium, pp. 270-74). 
" Cesium Radio-Isotope. A new Tool for Parts Inspection." By J. M. Thompson and P. A. 

Glenn. Iron Age, 1953, 172 (No. 11), 174-176. 
" Design and Performance Data of Space Ships with Ionic Propulsion Systems." By E. Stub- 
linger. Paper presented to the 8th International Astro-Nautical Congress, Barcelona, October, 

" Separation of Caesium and Strontium from Calcined Metal Oxides as a Process in disposal of 

High Level Wastes." By A. Abriss, J. J. Reily and E. J. Tuthill. Rep. 453 of April, 1957 from 

A.E.C., Brookhaven Nat. Labs. 
" Fission Products Recovery from Radio-active Effluents." By Moore and Burns. Paper 1768, 

Peaceful Uses of Atomic Energy Conference, Geneva, 1958 [Recovery of Caesium-137]. 
" Cesium: A New Industrial Metal." By A. J. Strod. Bull. Amer. Ceram. Soc, 1957, 36, 212-3. 
" The Preparation of Caesium and Rubidium Metals." By A. K. Lam and H. R. Foster, Jn. 

/. Amer. Chem. Soc, 1958, 14 pp. 
" Production of Kilo-curie Sources of Caesium-137." By B. F. Warner. Progress in Nuclear 

Energy, Series III, Process Chemistry, Vol. 2, 1958, pp. 487-500. 
" Rubidium and Caesium." By L. Hackspill, Nouveau Traite de Chimie Minerale. Ed. by P. 

Pascal. Paris, 1958, Vol. Ill, pp. 27-129. 
" Cesium Compounds." Product Information Leaflet Cs., American Potash and Chemical 

Corporation, 1959, 4 pp. 
" Rubidium Compounds." Product Information Leaflet Rb. American Potash and Chemical 

Corporation, 1959, 4 pp. 
" Cesium." By W. R. Barton, in " Mineral Facts and Problems." U.S. Bur. Mines Bull. 585, 

1960, 6 pp. 
" Rubidium." By W. R. Barton, ibid., 5 pp. 
" Minor Metals." U.S. Bur. Mines, Minerals Yearbook (Annual). 

Calcium Chloride (Natural) 

Although most of the calcium chloride required for industrial purposes is obtained 
as a by-product from chemical operations, only in some few localities is it remunera- 
tive to recover the salt, or calcium-magnesium chloride, from natural sources. This 
is particularly the case in certain areas of the United States. The peak production in 
the United States in recent years was in 1956 when shipments of solid and flake 
calcium-magnesium chloride (77-80 per cent. CaCk) totalled 531,561 short tons, 
whilst those of the salts in the form of brine (containing 40-45 per cent. CaCk) 
amounted to 183,229 short tons. In 1957 the corresponding totals were 535,618 
and 181,607 short tons respectively. The chief centres of production were in 
California, Michigan, Ohio and West Virginia. 

As a general rule, the salts are recovered from the mother-liquors which remain 
after the extraction of sodium chloride from some natural brines. In the past, two 
processes have been used for treating the mother-liquors, one having as its object the 
separation of calcium-magnesium chloride, whilst the second process yields calcium 
chloride, magnesium sulphate and calcium-magnesium chloride. For the production 
of calcium-magnesium chloride the bitterns are treated with milk of lime, settled and 
the clear liquid is evaporated to a thick syrup, which is run on to metal drums 
before it solidifies. The product, which consists of calcium-magnesium chloride, is 
then ground. 



In the second type of process, which has been used for treating brines for salt in 
Michigan, U.S.A., the original brines contain about 14 per cent, of sodium chloride, 
9 per cent, of calcium chloride, 3 per cent, of magnesium chloride and 0-15 per cent, 
of bromine. In this process, after the removal of much of the sodium chloride and 
bromine, the mother-liquors are treated with a suspension of magnesium hydrate, 
and after settling out the precipitate, the clear liquid is evaporated until some 
impure sodium chloride crystallizes out. The liquid, on cooling, deposits a double 
salt known as tachydrite (2MgCl2.CaCl2.12H 2 0) and the mother-liquor, which 
contains much calcium chloride, is reworked to give calcium chloride and mag- 
nesium sulphate. The tachydrite crystals are treated to recover magnesium chloride 
(MgCl 2 ,6H 2 0), and the mother-liquor from the treatment which contains equal 
proportions of calcium and magnesium chloride, is evaporated to a syrup and then 
flaked on a chip machine. 

The major part of the calcium chloride of commerce is derived as a byproduct 
in the Solvay process for the manufacture of sodium carbonate, in which process 
the chlorine for the calcium chloride is obtained from brine or rock salt and the 
calcium from limestone. Increasing quantities are obtained from brines. At 
Stassfurt, Germany, it is recovered by the potash companies from carnallite 
(KCl.MgCV6H.jO) which carried about 3 per cent. CaCl 2 . 


Most of the calcium-magnesium chloride recovered in the United States from 
natural sources is used for dust prevention on dirt roads and for soil stabilization. 
The addition of about 2 per cent, of calcium chloride to the weight of Portland 
cement used in concrete is stated to accelerate the curing time of lightweight con- 
crete blocks and to reduce breakage in early handling. Smaller amounts are used for 
laying dust in metalliferous mines, or for making heavy liquids used in coal washing. 
In cold climates a solution of calcium-magnesium chloride has been used for spray- 
ing ore shipments to prevent them freezing to a monolithic mass. It is also used in 
refrigerating brines and fire extinguishers. 

A.S.T.M. Specification No. D 98-56 T for calcium chloride to be used for dust- 
laying, stabilization, ice removal, acceleration of the set of concrete, curing of 
concrete, and other road conditioning purposes, provides for two types of material : 
Type 1, regular flake calcium chloride; Type 2, concentrated flake, pellet, or other 
granulated calcium chloride. The calcium chloride has to conform as regards 
chemical composition with the requirements shown in Table 42. 

Table 42 

Calcium Chloride for Dustlaying, etc. A.S.T.M., D 98-567 

Calcium Chloride, CaCla, min. 

Total alkali chlorides (as NaCl), max. . 

Total magnesium (as MgCla), max. 

Other impurities (not including water), max. 


er cent. 

Per cent 









Type 2 



The calcium chloride shall conform with the following requirements for particle 
size when tested by means of laboratory sieves. 

Sieve Percentage passing 

finch 100 

No. 4 (4,760 micron) not less than ... 80 

No. 20 (840 micron) not more than . . .10 

The calcium chloride may be rejected if it fails to conform to any of the require- 
ments of the specification, or if it has become caked or sticky in shipment. 

Hydrofiating load-carrying vehicle tyres filled with calcium chloride solution 
are claimed to give improved traction, increased draw-bar pull, reduced tyre wear, 
bounce and fuel consumption. A table listing size of tyre, weight of calcium to be 
used and other particulars has been given by P. C. Horgan in " Calcium Chloride 
Institute News " for January and February, 1958. 


" The Technology of Salt Making." By W. C. Phalen. U.S. Bur. Mines, Bull. No. 146 1917 
149 pp., including bibliography. ' 

" Calcium Chloride." By P. M. Tyler. U.S. Bur. Mines, Inform. Circ. No. 6781, 1934, 16 pp. 
Calcium Chloride in Cement." By D. A. Adams. Chem. Trade J., 1925, 76, 166-7 
Calcium Chloride, Quality Requirements for Industrial Drying." Anon. Chem. Trade J., 1932, 

" Reduction of Alkalis in Portland Cement— Use of Calcium Chloride." By E. R. Holden 

Industr. Eng. Chem., 1950, 42, 337-41. 
" Calcium Chloride as an accelerator for Prefabrication of Concrete." By J. Calleia Carrete 

Abstr. J. App. Chem., 1958 ii, 347. 
" Tests Prove Benefit (of CaCl,) in light-weight block." By H. A. Smith. Calcium Chloride Inst. 

News, Washington, 1956, 6 (No. 4), 6-7. 
" Liquid Filled Tyres Improve Traction." By P. C. Horgan, Calcium Chloride Institute News, 

1958, 8, Nos. 1 and 2. * 

" Calcium and Calcium Compounds." U.S. Bur. Mines, Minerals Yearbook (Annual). 


\rican Society for Test 

T.M. Standards, 1951. 

Calcium chloride for road purposes, acceleration of concrete and curing concrete. 

American Society for Testing Materials 
A.S.T.M. Standards, 1958 

D98-56 T. 


The only commercial ore of chromium is the mineral chromite, which has the theore- 
tical composition FeO.Cr 2 3 , corresponding to 68 per cent, of chromic oxide 
(Cr 2 03). Commercial ores, which may be termed chromite, chrome iron ore, etc., 
seldom contain much over 50 per cent, of chromic oxide owing to the replacement 
of part of the iron by magnesium and some of the chromium by aluminium. 

Chromite, which usually occurs as a dark brown or black mineral, may vary in 
specific gravity from about 4-6 for high chromium ore, down to about 4 for ore of 
low chromium content. It may occur either in lenses or tabular masses, or dis- 
seminated throughout the parent rock. Chromite is often found associated with 



other minerals, such as platinum, gold, titaniferous magnetite, nickel and cobalt 
minerals, magnesite, asbestos and talc. Chrome ore, as mined, may consist of 
grains of chromite embedded in a matrix of magnesium silicates. Chrome ore from 
primary deposits is usually capable of being marketed as mined, except, possibly, for 
some hand-picking. Disseminated ore, however, usually needs concentration to 
render it saleable. 

A useful generalization of the grades of chromite used for particular types of 
industry is afforded by some statistics published by the United States Bureau of 
Mines. These show that the content of chromic oxide (Cr 2 3 ) in the ore used in 
1 958 in that country for metallurgical purposes averaged 46 -9 per cent. ; refractories 
32-5 per cent.; chemical uses, 45-6 per cent. 

Considerable attention has been given in the United States to the possible 
recovery of chromium from low-grade ore by smelting in the electric furnace. 
Details of one such process, developed in the United States by the Bureau of Mines, 
are given by J. P. Walsted and electrolytic processes for the same purpose have been 
described by R. R. Lloyd and his co-workers. 

World Production 

The world's production of chrome ore in 1958 totalled about 3-7 million long 
tons, of which about 1 -28 million long tons came from British countries. The largest 
producers (those having outputs over 400,000 long tons) were the Philippine 
Republic, Turkey, Union of South Africa, the U.S.S.R. and Southern Rhodesia. 

The United Kingdom in 1958 imported for consumption 178,236 long tons of 
chrome ore, 25,791 long tons of ferrochrome, and 1,744 long tons of ferrosilicon 

The world's largest importer of chrome ore is the United States, which in 1958 
took 1,128,069 long tons of ore (containing 486,113 long tons of Cr 2 3 ), and 
ferrochrome containing 14,255 long tons Cr 2 3 . Most of these amounts were little 
more than half those for 1957. 

Turkish chrome ore, as exported, is usually of two grades containing 52-56 
and 44-51 per cent, of chromic oxide respectively. Southern Rhodesian ore is 
usually high grade with a content of chromic oxide varying between 48 and 51 per 
cent. The Union of South Africa produces ore from the Lydenburg district and the 
Rustenburg district with about 44-46 per cent, chromic oxide. The chrome ore 
exported from Greece is usually of low grade with 40 per cent, or less of chromic 
oxide and is employed mainly for making refractories. A high-grade ore containing 
over 50 per cent, of chromic oxide is produced in Baluchistan, Pakistan, and is used 
chiefly for metallurgical purposes, e.g. ferrochrome. Yugoslavian chromite has been 
marketed in two grades containing about 48 and 52 per cent, of the oxide respectively. 
Cuban ore is usually of low grade but has important uses for special purposes where 
a high alumina content is required. 

In Great Britain chrome ore was mined for some years on the island of Unst, 
one of the most northerly of the Shetland group. The ore mined carried up to 45 
per cent, of chromic oxide and was mostly sent to England for use in the manu- 
facture of chrome-magnesite bricks, 



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The industrial uses of chromite may be roughly classified, in order of consump- 
tion, under three headings: (1) as a component of ferro-alloys used in making alloy 
steels, such as armour plate, stainless and special cutting tool steels; (2) in refractory 
products for lining and repairing furnaces; and (3) in the chemical industry for 
producing chromates and bichromates from which, in turn, other chromium 
compounds are made. These compounds have many uses in tanning, dyeing, 
chromium plating and the manufacture of chrome pigments. The chemical industry 
normally consumes about 15-20 per cent, of the world's output of chrome ore. 

The composition of commercial chrome ores from various localities is shown 
in Table 43. 

Metallurgical Uses 

Chromium is used in metallurgy, principally in the form of its ferro-alloys, in the 
manufacture of various types of special steels. Metallic chromium is also used for 
the same purpose, but to a much smaller extent. Chromite for metallurgical pur- 
poses should normally contain at least 48 per cent, of Cr203 and the chromium/iron 
ratio should be not less than 2-8 to 1. Sulphur should not exceed 0-5 and phos- 
phorus 0-2 per cent. 

The importance of the chromium/iron ratio in metallurgical grade chrome ore 
is shown by the fact that of the tonnage used in the United States in 1956, in 69 per 
cent, the ratio was at least 3 : 1 ; in 26 per cent, it was less than 3 : 1 but not under 

2 : 1 and only 5 per cent, had a ratio of less than 2:1. 

Hard lump ore of about 6 in. size, with not over 10-15 per cent, through i-iri. 
screen, is usually preferred, but fines and concentrates are sometimes used. As a 
general rule, the combined percentages of alumina and magnesia should not 
exceed 25. 

Some chrome ores, which are unacceptable for metallurgical use on account of 
their ratio of chromium to iron falling below 2-8 to 1, are quite suitable for use as 
chemical ore. 

U.S. National Stockpile Specification P-l 1-R1, dated June 4th, 1956, for metal- 
lurgical grade chromite, for use in the manufacture of ferro-chromium and special 
chromium alloys, requires the ore to have the following composition before an offer 
will be considered: Chromic oxide, 48 per cent, (min.); chromium/iron, ratio 

3 : 1 (min.); silica, 8 per cent, (max.); sulphur, 08 per cent, (max.); phosphorus, 
04 per cent. (max.). All the above percentages are calculated on a dry basis. 
All chromite ore shall be lumpy and shall be hard, dense and non-friable material, 
of which not more than 25 per cent, shall pass a 1-in. sieve (A.S.T.M. designation 
E. 11). Chromite ore of a friable nature, regardless of an initially lumpy appearance, 
shall be rejected. 

Ferrochrome. The alloy most frequently used in the manufacture of chromium 
steels is ferrochrome containing about 70 per cent, of chromium and made either 
by the reduction of chromite in an electric furnace by means of carbon or silicon, 
or by the Thermit process. Two types of ferrochrome are marketed, known as 
" high carbon," which contains about 4 per cent, or more of carbon, and " low 



carbon," which may contain up to 2 per cent., but usually less. The specification 
issued by the A.S.T.M. is shown in Table 44. 

Table 44 
Ferrochrome, A.S.T.M. Specification, A 101-50 

High carbon 

Low carbon 

Chromium, Cr . . . 
Carbon, C .... 
Silicon, Si, max 

Per cent. 




Per cent. 


2-0 max.* 


* Provision is also made for types containing maximum percentages of carbon: 
2, 1, 0-5, 0-2, 015, 01, 006, 004. 

The U.S. National Stockpile Specification P-lla, of October 19th, 1954, 
requires that low carbon ferro-chromium shall have the following specified 
composition, by weight: a minimum of 65 per cent, chromium, and the following 
maxima: carbon, 010 per cent. ; silicon, 1 -50 per cent. ; phosphorus, 004 per cent. ; 
sulphur, 010 per cent. It shall be furnished in lumps, size 8 mesh or larger according 
to government specification. 

The U.S. National Stockpile Specification P-llb-R of October 19th, 1954, 
requires that high carbon ferro-chromium shall have the following specified 
composition by weight: chromium (min.) 65 per cent. ; carbon 40 to 60 per cent., 
and the following maxima: silicon, 1-50 per cent.; phosphorus, 04 per cent.; 
sulphur 010 per cent. It shall be furnished in lump size 1 in. or larger according to 
government specification. 

Increasing interest is being shown in lower chromium content ferrochrome 
alloys, since they are cheaper per lb. of contained chromium than the standard 
65 to 69 per cent, product. Of particular interest is charge-grade ferrochrome, which 
contains 20 to 60 per cent, chrome and up to 6 per cent, silicon and 8 per cent, 
carbon. It is made by the direct smelting of low grade iron-chrome ores. Charge- 
grade ferrochrome is currently used in the oxygen process of stainless steel making. 
It offers an economic advantage in the production of steels and its use may be 
expected to increase. 

Ferrochrome Silicon. Attention is being given to the use of ferrochrome silicon 
containing 31-39 per cent, chromium in the steel industry. 

The U.S. National Stockpile Specification P-llc-Rl of October 13th, 1956, 
requires that ferro-chromium silicon shall have the following composition by 
weight: chromium, 39 per cent, to 41 per cent.; Silicon 42 per cent, to 46 per 
cent.; with the following maxima impurities: carbon 05 per cent.; sulphur, 
05 per cent.; phosphorus, 05 per cent. All ferro-chromium silicon shall be 
furnished in lump size 8-mesh, or larger according to government specification. 

A process used by Murex Ltd. of Rainham, Essex, England, for the production 
of low-carbon ferro-chrome, containing 03-01 5 per cent, carbon, as described by 
J. A. Blake, consists essentially in treating a mixture of lumpy chrome ore, flint and 



coke in an electric furnace and so producing a high silicon ferrochrome containing 
over 45 per cent, silicon and substantially free from carbon. Into another group of 
furnaces of the submerged arc type is charged a mixture of washed chrome ore 
concentrates and lime to produce a synthetic " slag," which is tapped off. To this 
slag is added the secondary ferro-silicon-chrome referred to above in amount 
sufficient to reduce the Cr2C>3 content of the slag to about one-half and produce a 
low silicon, low carbon ferrochrome in accordance with the equation : 2Cr203FeO + 
4FeSiCr = CrsFe 6 + 4SiC>2. The silica produced in the reaction combines with the 
lime to give calcium silicate and the low-carbon ferrochrome settles in the bottom 
of the ladle. 

Chromium in Steel. For use in the manufacture of high-grade alloy steels, 
especially those of the stainless type, ferrochrome with as little as 0-06 per cent, 
of carbon is often specified. As low carbon ferrochrome cannot be made by reducing 
the ore with carbon, and the alumino-thermic process is stated to be too expensive, 
silicon is used as a reducing agent. 

Steels containing up to 3 per cent, of chromium are often utilized for rails; 
nickel-chrome steels, containing 1-3-75 per cent, of nickel, 0-45-1-75 per cent, of 
chromium and 1-0 -55 per cent, of carbon are employed in the automobile 
industry (the United States Society of Automobile Engineers have more than twenty 
different specifications for steels within these limits); steels with 3-12 per cent, of 
chromium are largely used for purposes which require good resistance to oxidation 
at high temperatures, such as in the tubes used in the oil-cracking industry; steels 
with 12-20 per cent, of chromium include the special class of stainless steels which, 
if of low carbon content, have great resistance to corrosion and oxidation. 

Chromium in Cast Iron. The addition of up to 1 per cent, of chromium to grey 
cast iron greatly improves its resistance to wear, while white cast iron containing up 
to 4 per cent, of carbon and 2 per cent, of chromium is useful on account of its 
resistance to abrasion. A chromium-boron-nickel cermet layer, as thin as 0-002 in., 
applied to ingot iron is reported to afford protection against oxidation for more 
than 800 hours at 1,500° F. 

Other Chromium Alloys. In addition to ferrochrome, a number of alloys of 
chromium with other metals are made for direct fabrication into articles for industrial 
use. The most important of these is the group of alloys known as " Stellites," the 
principal components of which are chromium, cobalt and tungsten. These alloys are 
considered under " Cobalt " (see p. 149). 

Alloys containing from 13 to 20 per cent, of chromium, 60 to 80 per cent, of 
nickel and the balance of iron are used for plant in the dairy and other food 
industries. One example of this class is " Inconel," which contains about 76 per 
cent, of nickel, 15 per cent, of chromium and the balance iron. This alloy offers 
good resistance to oxidizing conditions and to attack by many chemical compounds, 
including acids and alkalis at moderate concentrations. 

The constitution and properties of many alloys of chromium are dealt with by 
A. H. Sully in his book " Chromium " pp. 223-268. 

Chromium-boron, containing 20 per cent, of boron, 15 per cent, of aluminium 
and the balance chromium, is used as a coating constituent on hard-faced electrodes. 



Chromium carbides containing about 70 per cent, of the metal are being manu- 
factured by the General Electric Company in the United States. They are claimed 
to have high resistance to abrasion, corrosion and oxidation and to be good 
substitutes for tungsten carbide in cutting tools. 

Metallic Chromium. The methods used for the production of massive metallic 
chromium may be roughly grouped into (1) aluminothermic reduction; (2) silicon 
reduction; (3) electrolysis; (4) the carbon reduction process. 

In the aluminothermic method, which is exothermic, the raw materials are a 
fairly pure oxide of chromium and aluminium powder. The composition of the 
metallic chromium produced in several countries on a commercial scale by the 
aluminothermic process is shown in Table 45. 

Table 45 

Metallic Chromium produced by Aluminothermic Processes 





For use in 



special Ni-Cr 

Per cent. 

Per cent. 

Per cent. 

Per cent. 

Aluminium, Al . . . 





Iron, Fe 





Silicon, Si 





Carbon, C . 





Sulphur, S . 





Nitrogen, N 





Copper, Cu 
Lead, Pb . 




1 Spectro- 

Antimony, Sb 

J traces 

An account of the aluminothermic process as carried out in England at the 
Rainham plant of Murex Ltd. has been given by T. Burchell. 

The silicon reduction method, also an exothermic one, is often carried out in 
open arc electric furnaces which are lined with magnesia. The furnace charge 
consists of a mixture of finely divided chromic oxide and silicon in stoichiometri- 
cally calculated proportions in accordance with the equation. 

2Cr 2 3 + 3 Si = 4 Cr + 3 Si0 2 . 
Calcined lime is added to the charge to combine with the silica and so yield a fluid 
slag. The charge is fed into the furnace progressively and the slag decanted at 
intervals. The composition of the metal produced by the silicon reduction process is 
very similar to that obtained by the aluminothermic method, except that in the 
latter aluminium is present usually as a trace whereas in the former silicon is often 
rather higher; occasionally it may be as high as 2-5 per cent, if the chromium is 
required for use in making certain special alloys. 

In the electrolytic process, as described by R. R. Lloyd et al., the ore, ground to 
pass a 325-mesh screen is digested at 130-1 60° C. with a mixture of 93 per cent. 



sulphuric acid and some anolyte from the electrolytic cell, all the constituents in the 
ore, except the silica, being thereby dissolved. By a series of carefully controlled 
chemical operations the chromium is obtained in the form of ammonium chrome- 
alum, practically free from magnesium, calcium, titanium, vanadium and manganese, 
but containing about 0-78 per cent, iron and 05 per cent, aluminium. A solution of 
the alum is electrolyzed in a diaphragm cell to give metallic chromium containing 
about 03 per cent, sulphur, 1-0-4 per cent, iron and only spectroscopic traces of 
calcium, magnesium, aluminium, silicon, lead and copper. 

The carbon reduction process, which is used only to a small extent usually for the 
manufacture of special alloys, consists in reducing chromium oxide with com- 
mercially pure carbon in an electric arc furnace. An excess of carbon is usually 
employed so as to yield a metal containing some chromium carbide. 

A good resume of information concerning the physical properties of chromium, 
including its crystal structure, allotropy and lattice constants, is given by A. H. 
Sully in " Chromium, The Metallurgy of the Rarer Metals," pp. 63-104. 

The U.S. National Stockpile Specification P-96 of January 7th, 1957, requires 
electrolytic and exothermic chromium metal intended primarily for use in the 
production of high temperature and non-ferrous alloys to have the compositions 
shown in Table 46. 

Table 46 

Electrolytic and Exothermic Chromium Metal for use in the Production of High-Temperature 
and non-ferrous Alloys. U.S. National Stockpile Specification P-96, 1th January, 1957. 

Chemical Composition: 

Per cent, by Weight 

Chromium Or min. 

Iron Fe max. 

Aluminium Al , 

Carbon C „ 

Silicon Si „ 

Sulphur S 

Phosphorus P „ 

Lead Pb , 

Copper Cu „ 

Combined gases (Oxygen + Nitrogen + Hydrogen) . „ 


Nitrogen „ 

Hydrogen , 

Other elements, each , 


All electrolytic chromium metal is required to pass a 2-inch sieve and all exothermic 
chromium metal is required to pass a 1-inch sieve, A.S.T.M. designations. 

Chromium metal produced in Great Britain by Murex Ltd. includes two grades 
containing 98-99 per cent, and 99 per cent, (minimum) of chromium respectively, 
each grade having a maximum of 0-10 per cent, of carbon. 

Metallic chromium is used in the production of a wide variety of non-ferrous 



alloys, such as those used for electric resistance wires, corrosion-resistant alloys, 
non-ferrous metal cutting tools, welding rod tips and hard-facing materials. 

Refractory Products. Chrome refractory bricks may be made from the crushed 
ore moulded to shape with a binder and fired at a temperature not exceeding 
1,490° C. More generally, however, it is now the custom to add 5-50 per cent, of 
dead-burned magnesite to the mix. Such bricks have greater strength than ordinary 
chrome bricks and are more resistant to basic slags. 

Unlike many other refractories, chrome ore is nearly neutral from the chemical 
standpoint. It is composed of grains of chromite, which may constitute from about 
75 to 90 per cent, of the ore, embedded in a matrix of magnesium silicates. Although 
chromite itself has a high fusion point, probably in the region of 2,000° C, the 
matrix softens at a lower temperature, often between 1,260 and 1,420° C. 

Specifications for chromite for the manufacture of refractories vary, but as a 
general rule a low silica content is required. The chromite should be evenly distribu- 
ted through the ore and should not occur as coarse grains with aggregations of silica. 
The ore should be hard and in lumps over 12-mesh size. The content of CT2O3 is 
usually required to be over 40 per cent. Some users specify a content of 63 per cent, 
of alumina plus chromic oxide; a minimum of 57 per cent, is required by other users. 
The content of iron oxide and silica is sometimes limited to maxima of 10 and 5 per 
cent, respectively. 

As a general rule, the chromite should be low in serpentine, as the presence of 
this rock usually causes a decrease in strength at high temperatures. 

One Canadian user employs chrome ore carrying up to 25 per cent. Fe203, with 
AI2O3 up to 18 per cent, and SiC>2 not exceeding 4 per cent. As a general rule, 
however, large percentages of silica and iron are considered to be most objection- 
able in chrome ore intended for refractory use, as they tend to reduce the fusion 
point of the product. 

The U.S. National Stockpile Specification P-12-R1, dated July 1st, 1955, for the 
purchase of refractory grade chromite, requires the material to have originated from 
the Philippine Islands or Cuba, but ore from other sources may be considered. The 
chromite must be lump ore of which not more than 20 per cent, will pass a 10-mesh 
Tyler Standard screen or a U.S. Standard sieve No. 12. 

Ores from the Philippine Islands and from Cuba that conform to the following 
chemical requirements are acceptable: 

Per cent, by weight, 
dry basis. 

Chromic oxide, Cr20 3 , min. 310 

Chromic Oxide plus alumina Cr203 + AI2O3, min. . 60 

Iron, Fe, max. ......... 12-0 

Silica, SiOa, max. . . . . . . . .5-5 

Lime, CaO, max 10 

Magnesia, MgO, max. * 

* Not specified, but to be determined for each lot and reported. 

All other chromite ores shall conform to the physical requirements specified 


above and shall meet the requirements for satisfactory refractory properties as 
determined by tests performed at the direction of the Government, which will 
probably require some six months or a year. These tests, if performed, shall be on 
samples furnished by the offerer prior to purchase. Before such tests are performed, 
the offerer shall furnish proof acceptable to the Government that the deposits of 
chromite represented by his samples are of such size as to assure a satisfactory 

Chromium Compounds 

A number of chromium compounds obtained by the chemical treatment of 
chromite have important uses in industry. Such compounds include the chromates 
and bichromates of sodium and potassium, some chrome pigments and the com- 
pounds used in chromium plating. Manufacturers of chromates and bichromates 
vary considerably in their preference for chrome ore, some requiring high-grade ore, 
whilst others, who have worked out suitable processes, are using lower grade material. 
As a general rule, however, chemical manufacturers prefer high-grade ore, from 
which it is often possible to recover 95 per cent, of the chromium present; whereas 
an ore carrying only 40 per cent. Q-2O3 may yield as little as 35 per cent, of its 
chromium content. 

United States chemical manufacturers at one time employed principally ore 
from New Caledonia with some Rhodesian dyke ore and small amounts from 
India, but are now using Transvaal chemical grade (" B " friable) ore containing 
43^45 per cent. Cr203 (average 44-5), Si02 2-5-3-5 per cent, and having a Cr/Fe 
ratio of 1 -6 : 1 and an iron content too high for standard metallurgical use. French 
users formerly preferred New Caledonian ore, and before World War II Germany 
used Transvaal ore extensively in place of the Rhodesian or Indian chromite 
formerly employed. One British user expresses a preference for chromite con- 
centrates from Southern Rhodesia or the Transvaal with a Cr2C<3 content not below 
48 per cent, and only low percentages of silica and alumina. Some United States 
users specify a minimum percentage of 48 for chromic oxide, with silica not exceeding 
8 per cent., low sulphur and a Cr/Fe of about 1-6 : 1 . 

The U.S. National Stockpile Specification P-65, dated June 1st, 1949, for the 
purchase of chemical grade chromite, requires the mineral to contain not less than 
44 per cent. Cr2C>3 and not over 5 per cent. Si02. 

Processes for the production of chromates and bichromates Of sodium or 
potassium from chrome ore consist, essentially, of fusing the ore with alkali, 
separating the iron, alumina and silica and crystallizing and purifying the chromate 
or bichromate. 

In one process used in Germany the finely ground chrome ore is mixed with 50 
per cent, potash lye and sprayed into a rotary kiln fired with hydrogen. The fused 
mass is leached and the silica and alumina in solution are precipitated by agitation 
with carbon dioxide and potassium carbonate. The filtered solution is concentrated 
and impure potassium chromate crystallizes out. Potassium dichromate is obtained 
by redissolving the chromate in water, treating the solution with CO2 under pressure 
and cooling. 



In another process, the ore mixed with quicklime and soda ash is calcined in 
gas-fired, revolving-hearth furnaces at 1,000-1,180° C. By this means the silica 
and alumina are converted to insoluble compounds. The fused mass is leached 
with water, the solution treated with CO2 and cooled, whereby sodium 
bicarbonate separates out and sodium chromate is recovered from the solution by 

Sodium bichromate, NagCraO, . 2H2O, is the most important chromium chemical, 
as it forms the basis for most other compounds. The technical grade usually has a 
purity of about 99-8 per cent., with only about 06 per cent, of chlorides, calculated 
as chlorine, and about 0-2 per cent, of sulphates, calculated as SO4. 

Sodium bichromate is used in many metal treatment processes, such as pickling, 
etching or bright dipping of brass (to control the rates of reaction, such as the rates 
of solution of copper and zinc in brass) and in the acid cleaning of aluminium and 
magnesium. It is a constituent of most of the salt type preservatives for timber; is 
used as a mordant in dyeing textiles, as an oxidizing agent in dyestuffs manufacture; 
for bleaching waxes and for the purification of fats for use in soap manufacture; it 
is also employed for preventing corrosion in air-conditioning plant, refrigerating 
brines and diesel cooling systems, but sodium chromate may be employed if 
slightly alkaline conditions are necessary, e.g. in small air-conditioning plants, 
locomotive diesel engines, marine engines and mercury arc rectifiers. 

Sodium chromate, Na2Cr04, has industrial applications similar to those of the 
bichromate, but costs more. 

Potassium bichromate, K2Cr2C>7, can be employed for the same purposes as the 
sodium salt. It is anhydrous, non-hygroscopic and does not cake, and is, therefore, 
easy to handle in dry batch mixtures, such as are used in pyrotechnic products, 
safety matches and in some ceramic colours. The technical grade usually has a purity 
of 99-9 per cent., with only traces of sulphates and chlorides. 

Potassium chromate has properties similar to those of the sodium compound, 
but its use is limited by its greater cost. It has been used as a corrosion inhibitor in 
aluminium floats and in the fuel tanks of naval aircraft to prevent damage by the 
accidental entry of sea-water. It is also employed in some photographic chemicals 
and printing inks. 

Chromic acid is used chiefly as a constituent of chromium plating solutions and 
in the anodizing of aluminium (see p. 19). It is marketed in the form of technical 
flake or as powder, each containing about 99-8 per cent, of Cr 2 C>3 and sulphates 
equivalent to 01 per cent, as SO4. 

Pigments. A number of valuable pigments owe their colour and properties to 
chromium compounds. 

Chrome oxide green, which consists essentially of 97-99 per cent, of chromic 
oxide (0*203), is usually made by roasting sodium or potassium bichromate, either 
mixed with a reducing agent or in a reducing atmosphere. After cooling, the 
roasted product is washed to remove soluble salts, dried and ground. Chrome green 
is one of the most light-fast of all green pigments and is often used in protective 
paints, as it is unaffected by alkalis or acids in concentrations likely to be met with in 
normal use. It is also employed as a pigment in some printing inks, and is useful in 



rubber manufacture, as it will withstand any type of cure and has no tendency to age 
the rubber. 

Guignet's green, which consists essentially of hydrated chromium oxide, may be 
produced by calcining a mixture of sodium or potassium bichromate and boric acid 
at a high temperature. The fused mass is hydrolized with water and the insoluble 
pigment is separated and washed. This pigment has many of the properties of 
chrome oxide green but is more expensive to produce. It has great stability and 
permanence, but rather poor covering power. 

Other chromium pigments include lead chromate, which may vary in colour 
from lemon to orange, according to the method of manufacture; zinc chromate, 
which gives the yellow pigment zinc chrome or zinc yellow; and various green 
pigments produced from mixtures of Prussian blue and lead chromate or zinc 

Hexavalent chromium compounds containing zinc, cadmium or barium are 
valuable as corrosion inhibiting agents in paints, zinc yellow being the most widely 
used pigment for this purpose, particularly in priming coats for metals. 

British Standard Specification B.S. 318 : 1952 for green oxide of chromium for 
use in paints requires the pigment to contain not less than 98 per cent, of chromium 
oxide (Cr2C>3). The maximum for matter retained on a 240-mesh sieve is 1 per cent. ; 
matter volatile at 98-1 02° C. is limited to 0-5 per cent, and water-soluble matter 
must not exceed 0-5 per cent., the water extract being neutral to methyl red. 

A.S.T.M. specification D 263-46 for chrome oxide green requires the pigment to 
contain a minimum of 97 per cent, of chromic oxide (G-2O3) with a maximum limit 
of 0-5 per cent, for both matter soluble in water and moisture plus other volatile 
matter. The coarse particles retained on a No. 325 sieve must not exceed 2 per cent. 

A.S.T.M. specification D 212-47 for pure chrome green requires the pigment to 
be a precipitated mixture of lead chromate and iron blue (potassium or ammonium 
ferriferro-cyanide) with or without other insoluble compounds of lead. Extenders or 
diluents must be absent, and of the total lead present in the pigment not less than 
70 per cent, shall be present as lead chromate. Moisture and other volatile matter 
must not exceed 4 per cent, and matter soluble in water is limited to 1 per cent. 

Reduced chrome green according to A.S.T.M. Specification D 213-47 shall be 
a mixture of lead chromate and iron ferro-cyanide or ferri-cyanide blue, with or 
without other insoluble compounds of lead, precipitated on a base of barium 
sulphate or insoluble siliceous material or any admixture thereof. Its chemical 
composition shall be as follows : 

Per cent. 
Sum of barium sulphate and insoluble siliceous material, max. . 80 
Colour (total of insoluble lead compounds and iron blue) min. . 20 

Of the total lead (calculated as Pb) in the pigment the percentage present as lead 
chromate (PbCr04) shall not be less than 70 per cent. The total CaO present in any 
form soluble in acid shall not exceed 1 -0 per cent. Moisture and other volatile matter 
is limited to 1-0 per cent, and the coarse particles retained on a 325-mesh (44 
micron) sieve shall not exceed 1 -5 per cent. 



This specification has also been adopted by the American Standards Association 
as ASA— K28-1-1947. 

Chrome yellow and chrome orange pigment according to A.S.T.M. Specification 
D 21 1-47 may be one of the following five types of commercially pure lead chromate 
pigments: (1) primrose chrome yellow; (2) lemon chrome yellow; (3) medium 
chrome yellow; (4) light chrome orange; (5) dark chrome orange. The pigments shall 
be chemical precipitates of normal or basic lead chromate or mixtures of these with 
or without admixture with other insoluble compounds of lead, but without other 
admixtures, except those of reagent materials introduced specifically to improve 
those properties for which the pigment is used. The pigments shall be free from 
extenders (barium sulphate, clay, magnesium silicate, whiting, etc.) and shall 
conform as regards chemical composition to the requirements shown in Table 47. 

Table 47 
Chrome Yellow and Chrome Orange Pigments. A.S.T.M. D 211-47 








Lead chromate, PbCr04, min. 
Total water soluble matter, max. . 
Total of all substances other than 

insoluble compounds of lead, max. 
Moisture and other volatile matter, max. 
Coarse particles retained on a 325-mesh 

sieve, max 

Organic colours and lakes . 

Per cent. 



Per cent. 



Per cent. 



Per cent. 




Per cent. 



The above specification has been adopted in the United States by the Federation 
of Paint and Varnish Clubs as standard AS-8-52 and by the American Standards 
Association as ASA-K27-1-1947. 

British Standard Specification No. 303 : 1953, for Brunswick or lead chrome 
greens (pure and reduced) for paints applies to the composite pigments prepared 
from lead chromes and Prussian blue which are normally called Brunswick or lead 
chrome greens (pure and reduced) for use in paints. Material shall be in the form of 
a dry soft powder, or in such a condition that it may be readily reduced thereto by 
crushing under a pallet knife, without necessitating any grinding action. For the 
purpose of this specification the following definitions apply: 

(0 Lead Chromes. The yellow to near red pigments containing lead chromate, 
consisting wholly of insoluble compounds of lead and being free from organic 

(h) Prussian Blue. The blue product formed by the action of solutions of iron 
salts with ferrocyanide or ferricyanide solutions, with or without subsequent 
treatment with oxidizing agents. 

(a) Pure: (»') Material shall be free from organic dyestuffs when tested by a pre- 
scribed method and when dried at 98-102° C. for one hour shall consist wholly of 



lead chromes and Prussian blue of varying proportions in accordance with the 
colour desired, (ii) Where the desired colour requires the presence of co-precipitated 
aluminium compounds, the proportion of such compounds shall not exceed 4 per 
cent, calculated on the dry pigment and expressed as AI2O3. 

(b) Reduced. When a reduced quality is required, the proportion of pure 
Brunswick green and defined in (a) above, the inert extender to be used shall be 
specified by the purchaser and agreed with the vendor. The material shall not leave 
more than 1 -5 per cent, of residue on a 240-mesh B.S. sieve. The loss in weight on 
heating the material for one hour at 98-1 02° C. shall not exceed 3 per cent. The 
matter soluble in water when determined by the prescribed method shall not 
exceed 1 -5 per cent. The acidity of the aqueous extract when determined by the 
prescribed method shall not exceed the equivalent of 125 per cent, of sulphuric 
acid (H2SO4). 

The oil absorption value of the material, when determined by the prescribed 
method, shall be within ± 10 per cent, of the value of an agreed sample. The value 
of normal commercial grades of pure Brunswick green is usually between 10 and 50, 
that of reduced grades depending on the extent to which the pigment is reduced 
and the nature of the inert extender used. 

Corrosion Prevention. Sodium chromate is one of the most powerful corrosion 
inhibitors known. It finds extensive use for this purpose in closed water systems 
such as in boilers, refrigerating brines, air conditioning systems, cooling towers, 
diesel engines and automobile engines. 

There are a variety of metal treatments for aluminium, tin, zinc and cadmium 
plate which use sodium chromate. 

Gas and diesel engines are often protected against corrosion by the addition of 
chromates to the re-circulating cooling waters. It is stated that the best protection is 
obtained at pH in the range 7-0-9-5. Tests have shown that a concentration of 
500 p.p.m. sodium chromate is sufficient to give complete protection, but as the 
cost is relatively insignificant it is usual to employ a concentration of at least 1,000 

Calcium chromate, CaCrC>4, has been introduced, as a pigment in certain 
corrosion-inhibitive metal primers, particularly for magnesium and aluminium 
alloys. It is available commercially as a compound of 94 per cent, minimum purity 
and is stated to comply with the Ministry of Supply, Aircraft Material Specification 
D.T.D. 495. 

Chromic phosphate, CrP04.3H20, has been recommended for use in the so- 
called etching or wash primers designed to protect iron and steel surfaces from 
corrosion. Chromic phosphate can be formulated in a single pack primer with a 
synthetic resin, such as polyvinyl butyrate. 

Chromium Plating. This use of chromium is probably the one best known to the 
public, but, although of considerable importance, it does not represent a very large 
proportion of the total consumption of chromium. 

Chromium plating is an electrolytic process, the electrolyte consisting essentially 
of a solution of chromium trioxide containing a small quantity of sulphuric acid. 

In general, two classes of chromium plating are in common use in industry, (a) a 

M.C.A.I.— F 



very light deposit given for decorative or anti-tarnish purposes, and (b) a heavier 
coating which is applied to give resistance to wear and corrosion. 

The light coatings, which may range in thickness from 000001 to 000002 in., are 
usually deposited upon an undercoat of polished nickel or copper and nickel, 
because the chromium coating has but little protective power. Although such thin 
coatings are porous they are stated to be preferable to heavier deposits because, 
with increase in the thickness, stresses become greater, and it is stated that with 
deposits above 00002 in. in thickness coarse hairline cracking may ensue and 
extend downwards to reach the base metal. 

Heavy deposits, which may vary in thickness up to 0-01 in., are very hard and 
have good resistance to abrasion and corrosion, and for that reason are valuable on 
many types of chemical plant. Such heavy deposits of chromium are also useful for 
coating bearings, cams, slides and other machine parts where a low coefficient of 
friction is an advantage, or where good surface hardness is essential. 

Chromium has been extensively used for plating diesel engine cylinders and by 
the United States Naval Gun Factory at Washington for plating the bores of 

Electrodeposited hard chromium incorporating oil-retaining pores is used for 
reducing the wear on engine cylinder liners, piston rings, rolls, etc., the pores being 
obtained by suitable adjustment of the electrolyte and the cathode density. 

Chromizing is a process for giving certain metals, notably iron and steel, a 
protective surface coating of chromium, the chromium being introduced into the 
surface at a temperature at which it can diffuse into the underlying metal. Such 
coatings are firmly adherent, protective and resistant to thermal shock. A compre- 
hensive account of processes used for chromizing was given by R. L. Samuel and 
N. A. Lockington in 1951. Modern methods for treating iron are based on the 
action of chromous chloride in a reducing atmosphere. Thus, in the " B.D.S." 
(Becker, Daeves and Steinberg) process pieces of ferro-chromium mixed with 
crushed porous refractory are heated in a current of hydrochloric acid gas at 
1,050° C. to produce chromous chloride which is then absorbed in the pores of the 
refractory. When the reaction is complete the mass is cooled in hydrogen and is 
ready for use. The articles to be treated are packed in this chromizing compound and 
heated at 1,050° C. for five to ten hours. By this treatment the chromous chloride is 
volatilized and reacts with the iron surface by reduction and replacement. In 
another process, the"D.A.L." (Diffusion Alloys Ltd.), the operation is similar to the 
pack carburizing of steel. The articles to be chromized are packed into a specially 
designed receptacle (in which they can be protected from furnace gases) together with 
a chromizing mixture consisting of 60 per cent, of ferro-chrome (65 per cent, 
chromium), 0-2 per cent, ammonium iodide and 38-8 per cent, of unvitrified kaolin 
powder. The temperature of treatment varies between 800 and 1,100° C. according 
to the composition of the material being treated. A number of other methods have 
been devized for chromizing iron and steel but the two described above are those 
most commonly used on a commercial scale. 

Timber Preservation. Acid cupric chromate for use as a timber preservative by 
pressure methods is dealt with in South African Bureau of Standards Specification 



S.A.B.S. 43-1949, which requires that the solution in water shall have the following 

Sodium (or potassium) dichromate, calculated as Na 2 Cr 2 7 .2H 2 (min.), 
1 -5 per cent., (max.) 3 per cent. 

Copper sulphate, calculated as CuS0 4 .5H 2 (min.), 1-5 per cent.; (max.) 3 
per cent. 

Free acetic acid or free chromic acid should be present in quantity just sufficient 
to keep the salts in solution under operating conditions, i.e. 018 per cent. 

Dry " tanalith " for use as a preservative for the treatment of wood is dealt 
with in A.S.T.M. Specification D 1034-50, which requires the material to have the 
following chemical composition: 

Fluoride, calculated as NaF . 
Arsenate, calculated as Na 2 HAsC>4 
Chromate, calculated as Na 2 CrC>4 



Per cent. 

Per cent. 

. 22 


. 22 


. 34 




The minimum proportions may be as shown above, but the dry " tanalith " 
shall contain at least 95 per cent, of these active materials. The pH of a treating 
solution prepared from the " tanalith " shall be between 7-2 and 7-8. 

The above specification is identical in substance with that given in Section 3 of 
the American Wood-preservers' Association Standard Specifications for Salt 
Preservatives, P5-49. 

Tanning. The tanning of light leather probably accounts for quite a large pro- 
portion of chromium salts used in chemical industry. Two types of processes are 
used, which involve the employment of chrome-alum and sodium dichromate 

In the one-bath process, which is mostly used for tanning glove, garment and 
shoe-upper leathers, and for chrome retan sole leather, tanning is effected by means 
of basic chromic sulphate, which is obtained by the reduction of sodium bichromate 
by means of sodium thiosulphate, sodium bisulphite or an organic compound. In the 
two-bath method the prepared hides are soaked in an acidified solution of sodium 
bichromate and tanning is obtained by next immersing them in a solution of sodium 
thiosulphate, which reduces the bichromate to basic chromic sulphate. Chrome 
tanning has the advantage that the operation is only a matter of hours, as compared 
with days for vegetable tanning, but it is stated to produce a sole leather with 
exceptional wearing qualities, though rather deficient in water-resisting qualities. 

Other Uses. Although most of the chrome ore used in the chemical industry is 
taken for the production of chromates and bichromates, a small quantity of very 
finely-ground high-grade chromite is employed for special purposes. Air-floated 
chromite is used to give a smooth pearl-grey colour to floor tiles, or a bluish-grey 
tint to building bricks. Various shades of green may be imparted to glass by in- 
corporating 2-6 per cent, of air-floated chromite in the batch. 

r2 131 



" The Alloys of Iron and Chromium." Vol. 1 : " Low Chromium Alloys." By A. B. Kinzel and W. 
Crafts. New York, 1937, 535 pp. 

" Strategic Mineral Supplies." By G. A. Roush. New York, 1939, 473 pp. (Chromium, pp. 

" Chrome Ores as Used in the Refractories Industry." By T. R. Lynham and W. J. Rees. Trans. 
Ceram. Soc, 1939, 38, 211-25. 

" Alloys of Iron and Chromium." Vol. II. " High Chromium Alloys." By A. B. Kinzel and R. 
Franks. New York, 1940, 559 pp. 

" Chrome Ores and Chromium." By R. Allen and G. E. Howling. Rep. on the Min. Res. of Br. 
Empire and Foreign Countries, Imperial Institute, Lond., 1940, 118 pp., including biblio- 

" Refractory Materials: Their Manufacture and Uses." By A. B. Searle. 3rd Ed., Lond., 1940, 
(Chromite Bricks, pp. 520-31.) 

" Chromium." By D. C. McLaren. Pre-Cambrian, 1942, 25 (No. 12), 13-16. (Contains specifica- 
tions of ore for various purposes.) 

" A Survey of Important Base Minerals in Southern Rhodesia." By H. C. Milton. Mines Dept., S. 
Rhodesia, Bull. No. 2, 1943. (Chromium and Chrome Ore, pp. 47-65.) 

" The German Bichromates and Chrome Compound Industry." B.I.O.S. Final Report No. 265, 
Item 22, 12 pp. 

" Chrome Ore and Chrome-Magnesite Refractories." By J. H. Chesters. Iron Age, 1943, 152, 
Nov. 11, pp. 68-71 and Nov. 18, pp. 52-55. 

" Coloured Glasses." By W. A. Weyl. /. Soc. Glass Tech., 1944, 28, 158-266. (Chromium, pp. 

" Bichromates Manufacture (in Germany)." By F. H. McC. Berty and B. H. Wilcoxon. F.I.A.T. 
Final Rep. No. 796, 1946, 55 pp. 

" The Alumino-Thermic Process and the Preparation of Commercially Pure Chromium, Man- 
ganese and Special Alloys, such as Ferro-columbium." By T. Burchell. " Refining of Non- 
ferrous Metals." Inst. Min. Met., 1950, 477-504. (Chromium, pp. 492-5.) 

" Low-carbon Ferrochrome (0-03-0-15 per cent. C.)," by J. A. Blake. Ibid. pp. 505-515. 

" Stainless Steel and Iron." By J. H. G. Moneypenny. 3rd Ed., Lond., 1951. 

" Pilot Plant Production of Electrolytic Chromium." By R. R. Lloyd, J. R. Rosenbaum, V. E. 
Homme and L. P. Davis. Trans. Electrochem. Soc, 1948, 94, 122, and 1950, 97, 150. 

" The Protection of Metallic Surfaces by Chromium Diffusion." By R. J. Samuel and N. A. 
Lockington. Metal Treatm., 1951, 18, 407, 440, 495; 1952, 19, 27, 81. 

" A Critical Review of the Utilization of Transvaal Chrome Ore." By I. H. Kahn and A. M. 
Schady. /. Chem. Met. Min. Soc. S. Afr., 51, 247-260. 

" Chromium; Metallurgy of the Rarer Metals." By A. H. Sully. London, 1954, 274 pp. 

" Chromium." By M. J. Udy. Vol. 1. " Chemistry of Chromium and its Compounds," 433 pp. 
Vol. 2. " Metallurgy of Chromium and its Alloys." 402 pp. New York and London, 1956. 

" Electric Smelting of Low Grade Chromite Concentrates." By J. P. Walsted. U.S. Bur. Mines. 
Rep. Invest. 5268, 1956, 27 pp. 

" Electrolytic Production of Ductile Chromium." By E. Wainer. U.S. Patent 2,824,053, 1958. 

" Ductile Chromium." American Society for Metals. 1957, 376 pp. 

" The Radiochemistry of Chromium." By J. Pijck. National Research Council, Washington, 
D.C., U.S.A., 1960, 34 pp. 

" Chromium." By J. Amiel. " Nouveau Traite de Chimie Minerale." Ed. by P. Pascal. Paris, 

1959. Vol. XIV, pp. 33-551 (including 667 biblio. refs.). 

" Chromite." By H. A. Heiligman and H. M. Mikani. " Industrial Minerals and Rocks." Amer. 

Inst. Min. Met. Petrol. Eng. 3rd Ed., 1960, pp. 243-257. 
" One-Bath Chrome Tanning." (Chrometan). British Chrome and Chemicals Ltd., Stockton -on- 

Tees, 24 pp. 
" Chromium." By W. Mclnnis. " Mineral Facts and Problems." U.S. Bur. Mines Bull. 585, 

1960, 15 pp. 

Chemical Data Sheets: No.l, Chromic Phosphate; 2, Sodium Copper Chromate; 3, Potassium 
Tetrachromate; 4, Mercurous Chromate; 5, Copper Chromate; 6, Basic Chromic Chloride; 
7, Chromic Chloride Hexahydrate; 11, Calcium Chromate. British Chrome and Chemicals 
Ltd., Stockton-on-Tees. 

" Chromium." 17.5. Bur. Mines. Minerals Yearbook (Annual). 


American Society for Testing Materials 
A.S.T.M. Standards, 1958: 

Chrome Oxide Green, D 263-46. 

Chrome Yellow and Orange for Pigments D 21 1-47. 

Ferro-chromium. A 101-50. 

Pure Chrome Green. D 212-47. 

Reduced Chrome Green. D 213^*7. 

Zinc Chromate Yellow. D 478-49. 



British Standards Institution: 

Green Oxide of Chromium for Paints. B.S. 318 : 1952. 

Pigments for Colouring Cement, Magnesium Oxychloride and Concrete. B.S. 1014 : 1942. 
(Chromium Pigments, pp. 9-10.) 

Lead and Zinc Chrome for Paints. B.S. 282 : 1938. 

Brunswick or Lead Chrome Greens. B.S. 303 : 1938. 
U.S. National Stockpile Specifications: 

Chemical Grade Chromite. P-65, June 1st, 1949. 

Metallurgical Grade Chromite.P-11-Rl, June 4th, 1956. 

Refractory Grade Chromite. P-12-R1, July 1st, 1955. 

Chromium Metal. P-96, January 7th, 1957. 

Low Carbon Ferro-chromium, P-lla, October 19th, 1954. 

High Carbon Ferro-chromium, P-llb-R, October 19th, 1954. 

Ferro-chromium Silicon, P-llc-Rl, October 13th, 1956. 


Clay, according to the definition put forward by the American Ceramic Society, is a 
fine grained rock which, when suitably crushed and pulverized becomes plastic 
when wet, leather-hard when dry, and on firing is converted to a permanent rock- 
like mass. It is essentially a hydrated aluminium silicate. 

In view of the wide diversity in chemical composition, physical properties and 
industrial uses of the mineral products included under the term " clays," it has been 
decided to deal in this volume with clays under four headings: (1) China Clay, or 
Kaolin, (2) Ball Clay, (3) Fireclays and Refractory Clays, (4) Building-brick Clays. 
Clays used for the manufacture of Portland cement are dealt with in the " Lime- 
stone " section of this volume. The montmorillonite clays, bentonite and fullers' 
earth, whose principal uses are for purposes other than ceramics, are each given a 
separate chapter in this volume. 

Many ceramic clays need special treatment in order to render them suitable for 
industrial use. The treatment may comprise weathering, crushing and grinding, 
washing and possibly calcining. Weathering consists in exposing the quarried 
material to the action of rain, frost and sun for several months. This treatment is 
commonly applied to brick clays and shales worked in Great Britain. Crushing and 
grinding is sometimes used for material which consists of granular mineral bonded 
by an amorphous powder. The quality of many clays can be improved by converting 
them into a slip with water and sieving out the coarser material from the fine clay 
suspension. Further purification is also effected if desirable by partial sedimentation 
of the slip, thus causing more impurities to settle out. 

Unlike many other mineral substances, it is impossible to formulate any general 
specification for the purity of clay, as this depends largely upon the purpose for 
which it is to be used, e.g. white chinaware, earthenware, terracotta ware, building, 
engineering or refractory bricks, etc. Impurities in quantity which would be inad- 
missible for clay intended for one purpose may be quite desirable for other uses. 

A comprehensive account of the effects of the various components in clays used 
for ceramic purposes will be found in Searle and Grimshaw's " Chemistry and 
Physics of Clays," pp. 274-291. 




China clay, or kaolin, is a white powdery mineral which consists principally 
of a micro-crystalline compound approximating to the mineral kaolinite 
(Al2O3.2SiO2.2H2O). It has a specific gravity of 2-6 and a fusion point about 
1,785° C. 

It shows a refractive index of 1 -56 and is therefore virtually invisible in tricresyl 
phosphate. It is distinguished from other clays primarily by its whiteness, softness, 
ease of dispersion in water and other liquids, and freedom from impurities, par- 
ticularly iron compounds (less than 1 per cent. Fe203> and its negligible content of 
titanium and alkaline earths. The particle size range of the kaolin in the parent 
decomposed granite is from about 100 microns to 01 micron, but the products of 
commercial refining eliminate particles above 20 microns in the general run of 
standard grades and even of 5 microns in the finer grades of china clay. 

The micro-crystallinity of kaolinite is unusual in that while the smaller particles 
(under 1 micron) are 120° angle platelets, simple or slightly compound; the larger 
particles comprise stacks of platelets which appear as " vermicules " under the 
optical microscope. 

It should be noted that in Great Britain it is customary in scientific literature to 
reserve the name kaolin for material having the above characteristics and derived 
from the decomposition of felspar, but in the United States the term is often 
applied to many residual clays which give a white or nearly white product on burn- 
ing. Trade users in Great Britain almost invariably use the term china clay to 
designate material having the characteristic properties of kaolin, except for certain 
special products. A more important use of the term kaolin is for the grades specified 
in the British Pharmacopoeia. 

Pure kaolin would contain 46 per cent, silica, 40 per cent, alumina and 14 per 
cent, water. The finest commercial grades approximate closely to this, but ordinary 
grades, as now produced, contain up to 1 per cent, of Fe203, with traces of Ti02, 
CaO or MgO or Na20 and small quantities of K2O. 

World Production 

Material described as china clay is mined in many countries, but the largest 
producer of true china clay (kaolin) is Great Britain, where the output (practically 
all from Cornwall and Devon) rose from 789,908 long tons in 1952 to 1,212,981 
long tons in 1958. Exports from the United Kingdom also rose from 458,409 long 
tons to 754,153 long tons. Clays classified as china clay are produced in other 
countries, the largest outputs being obtained in the United States, Federal Germany, 
Austria, India, Algeria, France, Spain, Italy and Australia. 


English china clay is produced from opencast mines by a hydraulic system and is 
processed by a whole series of very specialized operations to give a highly refined 
product of reliable properties. The product of each mine exhibits characteristic 
properties that are important for the various industrial uses, but the modern ten- 



dency is to produce standardized products from a group of mines with an elabora- 
tion of instrumental controls to maintain the desired properties. 

Prepared china clay is used in paper, ceramics, rubber, plastics, paint, pharma- 
ceuticals, polishes, ultramarine, oilcloth, insecticides and fertilizers, textiles and in 
many other industries. 

Paper. The importance of china clay in the manufacture of high class papers is 
not generally realized by the public. About 60 per cent, of the china clay produced 
in Cornwall is consumed by the paper industry. 

Nearly all paper manufactured contains china clay in amounts varying from 5 to 
35 per cent, calculated on the weight of the fibres, the exceptions being banknote 
paper, high grade kraft and papers that have to wear well with long and constant 
use. Clays are produced to various degrees of fineness depending on the class of 
paper being manufactured. The more common grades of china clay are used as 
fillers to keep down costs, as the fibrous raw materials, which are the basis of the 
paper, are much more expensive than china clay. At the same time, the clay imparts 
desirable properties to printing paper, such as reduced expansion while printing, 
flatter paper, better opacity and smoothness. The finer varieties of white china clay 
are used for coating the surface of papers known as art papers and chromes. There 
are specially produced clays controlled to a very rigid specification regarding par- 
ticle size, Theological properties, etc., which are solely used in the production of 
machine coated papers. 

According to C. G. Albert the development of machine coating of paper has 
made it necessary to operate at much higher speeds, with resulting changes in 
specifications for china clay used for coating. Among the requirements is the 
demand for china clay with particles of relatively flat plates of 2 microns or less and 
the use of a clay slurry for coating containing 60-70 per cent, of solids, as compared 
with 30-^M) per cent, used previously. 

Pottery. Requirements for ceramics cover particle size, plasticity, strength, 
deflocculation behaviour and chemical composition before firing. It is also examined 
for whiteness, vitrification, porosity and contraction after firing under controlled 
conditions corresponding to manufacturing conditions. In general, British users 
prefer that the clay should be free of mica larger than 20 microns and completely 
free of quartz and iron-bearing minerals. English china clays contain 37 to 39 per 
cent, of alumina and 46 to 47 per cent, of silica and have a loss on ignition of about 
12-5 per cent. The content of iron as Fe203 ranges from 0-4 to 1 per cent, and that 
of titanium dioxide is less than 1 per cent. Potash (K2O) ranges from 1 to 2 per cent, 
in the various grades and governs the degree of vitrification on firing. As regards 
grain size, this varies from about 20 to 60 per cent, under 1 micron in diameter 
and this can affect the suitability of a given clay for the various forming pro- 

Paint. China clay is not largely used as a pigment in oil paints owing to its high 
oil absorption (30-45) and its poor opacity in oil, due to its refractive index (1 -56) 
being very close to that of linseed oil. It is, however, sometimes used as an extender 
or suspending agent in oil paints, and, fairly extensively, as a pigment in water 
paints or distempers. 



British Standard Specification B.S. 1795 : 1952 for Extenders for Paints desig- 
nates two grades of china clay for this purpose, having the following compositions : 

Grade 1 
Grade 2 

Total Residue on Sieve 


B.S. sieve 


Per cent. 


B.S. sieve 


Per cent. 


98-102° C. 

Per cent. 




in water 


Per cent. 

Acidity or 

alkalinity * 


Per cent. 

Loss on 
ignition (of 
dried mater- 
ial) at 900° C. 

Per cent. 

* Calculated as H 2 S0 4 or Na 2 CO s . 

If intended for use in oil paints, the clay should also be tested for its behaviour 
when mixed with the vegetable oil which is to be used in the paint, as some white 
clays, under these conditions, turn darkish. 

Specification D 603-42 of the American Society for Testing Materials, for 
aluminium silicate pigments (china clay), requires the chemical composition to be 
within the following percentage limits: Si02, 43-47; AI2O3, 37-40; loss on ignition, 
10-15; moisture and other volatile matter not exceeding 1 per cent. The coarse 
particles retained on a 325-mesh sieve must not exceed 2 per cent. 

The composition of kaolin for use in distemper and paints is given in South 
African Bureau of Standards Specification S.A.B.S. 442-1953, which provides for 
three grades — white, greyish white and yellowish white. The requirements for all 
three grades as regards chemical composition and physical properties are as follows : 
moisture and volatile matter (at 105-1 10° C. for two hours) 2 per cent, (max.), 
loss on ignition on moisture-free sample 10-14 per cent. ; matter soluble in a 2 per 
cent, solution of hydrochloric acid 01 per cent, (max.); acidity or alkalinity of the 
aqueous solution (expressed as H2SO4 or Na2C03) 01 per cent, (max.) 

Textiles. China clay is commonly used in the textile industry, in conjunction with 
suitable binders, to give weight and body to cloth. For this purpose the clay should 
be pure white in colour and quite free from any yellowish tint or added colouring 
matter, such as ultramarine. Grit is most objectionable as it may cause broken 
threads during manufacture. The presence of grit may be detected by rubbing a thin 
cream of the clay between two sheets of glass or by more detailed elutriation tests. 
Calcium carbonate and iron oxide are also objectionable and not more than a trace 
of these compounds should be present. The texture, or feel, of the clay when made 
into a thick paste with water is regarded by some users as a useful criterion of its 

Of all the mineral products used in finishing textiles, china clay has the best 
covering power. 

Refractories. " Molochite " is a highly calcined aluminium silicate made from 
specially prepared kaolin, low in alkalis and in iron, by English Clays, Lovering, 
Pochin & Co. of St. Austell, Cornwall, England. They state that by suitable heat 
treatment the kaolin is converted into a highly stable refractory showing almost the 
maximum development of crystalline mullite — practically 96 per cent, of the maxi- 



mum possible as indicated by chemical analysis. The composition range of Molo- 
chite is shown in Table 48. 

Table 48 

Analysis of " Molochite " Refractory 

Per cent. 

Silica, SiO a 54-55 

Alumina, AI2O3 42 ~* 3 

Ferric oxide, FeaOs 0-75 

Titania,TiOa 008 

Lime, CaO 01 

Magnesia, MgO 0-1 

Potash, K2O 1-5-2-0 

Soda, NaaO 01 

It is claimed that for many purposes refractories incorporating Molochite 
will be less costly, but will give service equal to most other refractories in the 42-72 
per cent, alumina range. The material is available in a number of controlled grades 
suited to a wide range of manufacturing techniques to give alumino-silicate re- 
fractories at firing temperatures generally employed. The gradings available range 
from " superfine " with 45 per cent, of particles below 2 microns, 21 per cent, 
below 1 micron and 1-4 per cent, above 10 microns, up to material within the 
grading £ in.-8-mesh. It is claimed that Molochite if suitably bonded can be used 
for making a wide range of refractories suitable for use in the glass, ceramic, and 
iron and steel industries, also in refractory fire cement, foam insulating concrete and 
dense refractory concrete. 

Oilcloth. For use as a filler in the manufacture of oilcloth, the clay should 
" slake " easily to a thin cream, or slip, without leaving lumps, be free from grit, 
have a good white colour and a relatively low oil absorption. 

Rubber and Plastics. China clay is an important filler for general purpose rubbers 
where it provides reinforcement properties. For articles like rubber hose about 
50 per cent, is used, but where extra hardness and stiffness are required, as for ex- 
ample in flooring, larger proportions are used. Specially treated clays are used in 
certain types of synthetic rubber and plastics for improving the electrical properties 
of the compounds. 

Experiments made on a number of British china clays, both ordinary and specially 
prepared, have shown that their use in rubber compounding mixtures considerably 
increases the tensile strength of a basic mix when added in amounts less than 18 
per cent, by volume of the rubber used. 

Catalysts. Selected deposits of kaolinite and halloysite, two of the kaolin 
minerals, are used as catalysts in the petroleum industry in the United States. These 
natural clay minerals are treated with acid and heated to give a catalyst similar to a 
synthetic alumina-silica gel catalyst. 

Ultramarine. China clay for use in the manufacture of this colouring matter 
should be low in iron oxide and lime and should not contain any large amount of 
free silica (quartz). 



A.S.T.M. Standard specification for ultramarine blue, D 262-47, requires the 
material to be produced by calcining a mixture of clay and silica with sodium salts, 
sulphur and carbonaceous material. It shall be a soft, dry, finely ground powder of 
good blue colour, free from admixtures of colour substances and shall conform to 
the following requirements: matter soluble in water, max., 1 -5 per cent. ; moisture 
and other volatile matter, max., 4 per cent.; coarse particles retained on No. 325 
sieve, max. 1 per cent. ; organic colours or lakes, none. 

Insecticides. China clay is probably the most widely used distributing agent for 
insecticides. It is valued for this purpose on account of its fineness, non-abrasive 
and floating properties and its freedom from harmful constituents, such as arsenic. 

Specially Prepared China Clays. In addition to the high grades of china clay 
normally produced in Great Britain, there is a fair output of specially refined 
products from Cornwall and Devon. The processing used for these materials is often 
concerned both with obtaining a very high percentage of kaolin in the finished 
product and with producing grades of special particle size and texture. For example, 
" Supreme " kaolin has 75 per cent, of its particles not over one micron and practic- 
ally all particles smaller than 10 microns diameter. On the other hand, " Talcolite " 
has had most of its finer particles removed and has only 3-4 per cent, below one 
micron. Grades intermediate between " Supreme " and " Talcolite " are also 

" Stockalite " is a colloidal china clay similar in many respects to " Supreme," 
but has the property of remaining much longer in suspension in liquids. 

" Osmosed " china clay, produced by electro-osmosis, is a highly refined product 
used in the manufacture of optical glass, refractory porcelain, rubber and for 
certain medicinal purposes. 


The term " ball clay " is usually applied to plastic, sedimentary clays which 
burn to a good white colour. Their principal use is for adding to kaolin to give 
strength to the fired body whilst maintaining the white colour. 

In Great Britain large deposits of ball clay are worked in North and South 
Devon and Dorset, the products being widely used in the domestic whiteware 
industry and considerable quantities exported. Ball clays occur in other countries, 
but are not common. In the United States the ball clays produced in Tennessee and 
Kentucky much resemble those mined in the United Kingdom. Few foreign occur- 
rences, however, are of the high quality of the British material. 

As a general rule, chemical analysis shows ball clays to be richer in silica and 
poorer in alumina than china clay, but they usually contain larger percentages of 
alkalis, iron oxide and carbonaceous matter. According to Searle the percentage 
composition of ball clays usually falls within the following limits: silica, 45-60; 
alumina, 25-35; loss on ignition, 7-15; iron oxide, < 2; lime and magnesia, < 1 ; 
alkalis, < 3. 

According to D. A. Holdridge, the mineralogical composition of ball clays from 
Devon and Dorset may be assumed to be as shown in Table 49. 



Table 49 

Mineralogical Composition of Ball Clays 

North Devon 

South Devon 


Kaolin type 
Quartz . 
Organic matter 

Per cent. 



Per cent. 


Per cent. 





South Devon ball clays occur in a basin about 9 miles long and 3 miles wide 
near the town of Newton Abbot, and reach a depth of approximately 1,000 ft. 
in the centre of the basin. The deposits, which have been worked since about 1750, 
produced over 200,000 long tons in 1957. Between 30 and 40 different types 
of clay occur in the deposit and, by careful selection in mining, 25 different grades of 
clay can be marketed. 

South Devon ball clays are of the carbonaceous type, with low, or medium, 
felspar content and little free quartz. The clay substance is principally kaolinite, but 
small amounts of halloysite appear to be present. The grain size of the clay substance 
is very small, some 75-85 per cent, of the particles being less than ^-^^ mm. in 
diameter. This low grain size is one of the main reasons for the high plasticity and 
bonding strength of the clays. The range of clays includes both vitreous and semi- 
refractory types. The clays are free from soluble salts, siderite and pyrites; any iron 
present occurring as hydrated ferric oxide. 

At the South Devon ball clay quarries, although modern excavating machinery 
is used to remove overburden, the actual clay is dug by hand so that a selective 
separation can be made of the several grades of clay available. At one time it was 
customary to " weather " the ball clay by allowing it to stand in large conical heaps, 
each containing from 200 to 500 tons, exposed to the weather for long periods. 
Research work carried out at the mines, however, has shown that better products 
can be obtained by mechanical shredders and ball clay, shredded and partly dried 
is now accepted by potters as the most suitable form in which to take their clay. 

Shredded clay is available in sizes varying from 1J in. to dust; it blunges very 
readily with water and is more easily handled than the old type of clay in balls. 

A survey carried out by the British Ceramic Research Association, and in parti- 
cular work by Holdridge, has contributed much to the knowledge of the properties 
of South Devon ball clays. This work has enabled South Devon ball clays to be 
classified into four distinct groups. Group 1, extra white clays, which are noted for 
their fine casting properties, producing fluid stable casting slips having very low 
thixotropy at optimum deflocculation. A full account of these clays will be found in 
the lecture given by V. R. G. Ashcroft-Hawley to the British Pottery Managers' 
Association. Group 2 clays, termed dark blue, have similar properties to those of 
Group 1, but impart a high degree of strength to cast bodies. Group 3, light blue, 
are rather less fluid and more thixotropic than those of Groups 1 and 2. Group 4, 
high silica, are in general similar to those of Group 3 but cast more rapidly. A 



number of standard blends adapted for particular ceramic purposes are marketed 
by the producers. 


The characteristics which make first quality ball clays of especial value to the 
ceramic industry are their exceptional whiteness when fired, high plasticity and 
strength, freedom from specking and soluble salts, and excellent behaviour in cast- 
ing slips; properties which make them essential components of casting bodies, 
whether for thick sanitaryware or thin tableware. In addition, most clays in the 
group are very resistant to cracking when incorporated in dust-pressed tile bodies, 
thus making them a valuable ingredient for conferring simultaneously both white- 
ness and resistance to firing loss. Some ball clays form the main part of the clay 
addition in pottery bodies for tableware, fancy goods, white wall tiles and electrical 
porcelain, whilst others are especially suitable for iron enamelling clays, bonding 
clays for refractories and abrasive wheels, faience and stoneware manufacture, 
bonding of foundry sands, fillers for paint and rubber and numerous other uses. 
Some clays are almost completely vitreous when fired at 1,200° C, whilst others are 
relatively refractory at that temperature. 


Fireclay may be described as an earthy, plastic, detrital material in which 
the percentages of iron oxide, lime, magnesia and alkalis are sufficiently low to 
enable the material to withstand a temperature of at least 1,500°C. and preferably 
over 1,600° C. Fireclays occur widely distributed and are of variable composition. 
They can, however, be roughly divided into three types : (1) flint clays, which usually 
occur as rocklike masses; (2) plastic clays, which can be broken down by water into 
a mouldable plastic mass; (3) shales. 

In Great Britain fireclays are usually found in close association with coal seams 
of the Carboniferous age, particularly in Northumberland, Durham, Yorkshire, 
Worcestershire, Staffordshire and in various localities in Scotland and Wales. 

The chemical composition of fireclays can vary between wide percentage limits, 
e.g. silica, 40-80; alumina, 10-40; iron oxide, 1-5; loss on ignition, 5-14. Alkalis are 
usually less than 3 per cent, and lime and magnesia less than 5 per cent. As a general 
rule the higher the alumina content the greater the refractoriness. 

The chemical analysis of a fireclay affords a useful indication of its possibilities 
as a refractory, but the criterion is a test under practical working conditions. In 
general it may be stated that the higher grade fireclays do not usually contain more 
than 3 per cent, of alkalis, or over 2 per cent, of iron oxide. The desirable physical 
characteristics include the ability to yield refractory ware which is devoid of 
shrinkage and shows good resistance to abrasion and corrosion by the furnace 
charge under working conditions. 

Chemical analyses of the fireclays from the main producing areas in the United 
Kingdom, quoted by Searle and Grimshaw, show a wide variation in composition 
even in material from the same area; this variation is illustrated in Table 50, which 
gives some analyses of material from the more productive seams. 



Table 50 

Analyses of some British Fireclays* 
Per cent. 


Durham and 

South Wales 


and Shropshire 












Silica, SiO, 











Alumina, Al s O s 











Ferric oxide 
Fe s O, 











Titania, TiO, 











Lime, CaO 











Magnesia, MgO 



0-2-1 -2 








Soda, Na,0 











Potash, K s O 











Loss on ignition 











* From " The Chemistry and Physics of Clays," by A. B. Searle and R. W. Grimshaw, 3rd Ed., London, 1959. 

The behaviour of a clay when used as a refractory material is largely dependent 
on the composition of the individual minerals present and their grain size distribu- 
tion. The nature of the individual minerals present in a clay and their behaviour 
when heated has an important bearing upon its refractory properties. Much 
information on the mineralogical composition of a number of British fireclays is 
given by R. W. Grimshaw, K. Carr and A. L. Roberts in Trans. Brit. Ceram. Soc, 
1955, 51, 334. 

In recent years there has been an increasing demand for refractory bricks capable 
of withstanding higher temperatures than was formerly the case, and this has been 
met by the production of so-called super-duty fireclay bricks. According to Searle 
and Grimshaw the range in percentage composition of high alumina fired bricks is 
as follows: Silica, Si0 2 , 45-51; Alumina, A1 2 3> 39-48; Iron oxide, Fe 2 3 , < 2; 
Titanium dioxide, TK) 2 , about 2; Lime, CaO, < 0-5; Magnesia, MgO, < 0-5; 
Potash and Soda, K 2 0, Na 2 0, < 1 -5. 

A useful classification of fireclay and high alumina refractory bricks is given in 
A.S.T.M. Tentative Specification No. C 27-58 T, which deals with the products 
under six headings, as shown in Table 51. 

The properties enumerated in the above classification have to be determined 
according to the following methods of test: 

(a) Pyrometric Cone Equivalent — Method of Test for Pyrometric Cone Equiva- 
lent (P.C.E.) of Refractory Materials (A.S.T.M. Designation C 24). 

(6) Reheat Test for Super Duty Brick (2,91 0°R, 1,600° C.)— Schedule C of the 
Method of Test for Reheat Change of Refractory Brick (A.S.T.M. C 1 13). 

(c) Panel Spalling Loss for Super Duty Brick (3,000° F., 1, 650° C.)— Method of 
Panel Spalling Tests for Super Duty Fireclay Brick (A.S.T.M. C 122). 

(d) Load Test (2,460° F., 1,350° C.)— Schedule 2 of the Method of Testing 
Refractory Brick under Load at High Temperatures (A.S.T.M. C 16). 

(e) Modulus of Rupture— Method of Test for Cold Crushing Strength, or 
Modulus of Rupture of Refractory Brick and Shapes (A.S.T.M. C 133). 



Table 51 

Fireclay Refractory Brick classified according to Classes and subdivided into Types. 

A.S.T.M. C27-58T 



High duty 


Medium duty 
Low duty 

High alumina 




I Slag 



I Slag 

' 50 per cent, 

60 per cent, 

70 per cent, 

80 per cent. 
, alumina 













Loss max. 

per cent. 

8 at 
3,000 °F. 

4 at 
3,000° F. 

10 at 
2,910° F. 

Hot Load 

per cent. 

1-5 at 
2,460° F. 


per cent. 

10 at 
2,910° F. 

10 at 
2,910° F. 











Other Test 

Bulk density, min. 
140 lb. per cu. ft. 

Bulk density, min. 

137 lb. per cu. ft., or 

max. porosity 15 per 


Silica content, min. 

72 per cent. 

Alumina content 50 
±2 -5 percent. 

Alumina content 60 
±2*5 per cent. 

Alumina content 70 
±2-5 percent. 

Alumina content 80 
±2-5 per cent. 

(f) Bulk Density (weight per cu. ft.) — Methods of Test for Size and Bulk Density 
of Refractory Brick (A.S.T.M. C 134). 

(g) Silica and Alumina Content — Standard Methods of Chemical Analysis of 
Refractory Materials (A.S.T.M. C 18-52). 


The physical properties of these clays are usually of more importance than their 
chemical composition. The most essential physical characteristics are that the clay 
shall be sufficiently plastic to enable it to be easily moulded into the required shape, 
that it shall retain that shape in both the wet and dry states, and that it shall be 
capable of being sufficiently vitrified at 950-1,100° C. to form hard bricks without 
excessive shrinking or deformation. 

In considering the economic possibilities of a clay for brick making it is necessary 
for the deposit to be readily accessible and sufficiently extensive to allow for large- 
scale production. According to Searle and Grimshaw, for an output of 10 million 
bricks per annum for 20 years there must be available 800,000 cubic yards of suit- 
able excavatable material; this, at an average thickness of 3 yards, would occupy 
an area of about 55 acres of land, apart from that needed for margins and the works. 



As regards chemical composition, clays suitable for making building bricks 
usually contain about 8 per cent, of alkalis, but in some the amount may be as high 
as 15 per cent. Calcium compounds, if finely divided, may be useful in some clays 
rich in iron. 

Soluble salts, such as sulphates and chlorides, are objectionable as they may 
cause the formation of a white efflorescence or " scum " on the surface of the brick 
when it is exposed to the weather. This defect may not become evident until some 
little while after the brick has been exposed to a moist atmosphere. In order to 
overcome this defect, barium carbonate is sometimes added to the clay before 

A useful classification of the many types of clay used in Great Britain for the 
manufacture of building bricks has been given by D. G. R. Bonnell and B. Butter- 

The clay as quarried does not usually contain sufficient water to enable it to be 
moulded into bricks or many other ceramic bodies. It is therefore incorporated with 
a certain proportion of water, the quantity depending upon the nature of the clay 
and the process to be used for forming the shapes. 

The processes used for making building bricks may be roughly classified into: 
(1) wire cut methods; (2) stiff plastic, or stiff mud, processes; (3) semi-dry processes; 
(4) dry pressed methods. 

The finishing temperature for burning building brick varies with the composition 
of the clay used, but the following may give useful indications of the range. 

Red bricks and tiles rich in lime . . 790-1 ,080° C. 

Red bricks and tiles free from lime 
Glazed bricks .... 
Vitreous tile .... 
Salt glazed bricks, drainpipes, etc. 

1,100-1,300° C. 
1,200-1,280° C. 
1,180-1,200° C. 

Space does not permit of a description of the methods used in brickmaking, but 
full details will be found in A. B. Searle's " Modern Brickmaking" and Searle and 
Grimshaw's " Chemistry and Physics of Clays." 

Clay suitable for the manufacture of engineering bricks is of a similar type to 
that used for making ordinary building bricks, but usually contains a rather larger 
percentage of fluxing agents, which facilitate the production of a stronger, harder 
and more impervious brick. 

Engineering bricks are characterized by their high strength and impermeability 
to water and are usually hard and dense as defined by British Standard Specification 
B.S. 1301 : 1946. They usually have a mean compressive strength greater than 7,000 
lb. p.s.i. and less than 7 per cent, of water absorbed under the boiling test. 

British Standard Specifications dealing with clay products include B.S. 
1301 : 1946 for clay engineering bricks; B.S. 1190 : 1944 for hollow clay building 
bricks; B.S. 1286 : 1945 for clay tiles for flooring, and B.S. 402 : 1945 for clay 
roofing tile. 

Specifications issued by the American Society for Testing Materials include 
C 62-44 for building bricks. 




In recent years considerable use has been made of the so-called " bloated " or 
expanded clays and shales as lightweight aggregates for concrete. In the United 
States an extensive research programme on the preparation and use of such materi- 
als, started in 1953 at the University of Toledo, Ohio, has been continued by the 
Expanded Shale Institute of Washington, D.C. Many firms are producing such 
aggregates by the use of sintering machines. Lightweight aggregates are produced 
from clays which are either natural bloating, or are amenable to mixing with fuel 
oil, coal or other combustibles. Firing is done in rotary kilns or sintering machines. 
Shales and clays containing either illites, montmorillonites or chlorite-vermiculite 
minerals are the most promising sources of lightweight aggregates. Presence of a 
large amount of kaolinite will cause the material to be too refractory for economic 

The production of lightweight concrete aggregates from colliery waste and shales 
has been carried out in Great Britain by the Leftwich sintering process, as described 
by F. Catchpole. The patent rights of the process were acquired by Messrs. Aglite 
(Great Britain) Ltd., who worked the process for a time using shale as a raw material, 
but more recently have changed over to a mixture of brick-clay and fuel. This type 
of sintering machine will make lightweight aggregate from a wide variety of clays 
and shales. The shale previously employed by Aglite Ltd. had the following per- 
centage composition: Si0 2 , 4306; CaO, 0-39; Fe, 3-51; volatile combustibles, 
11-35; fixed carbon, 11-55. Clays or shales containing less carbon, such as those 
used for brickmaking, are suitable for sintering if the carbon content is increased by 
the addition of coke or anthracite dust. A loamy non-carbonaceous clay may require 
as much as 7 per cent, by weight of coke. The material to be sintered, when on the 
sinter grate, must form a permeable bed and in order to do so it is first ground to 
dust, water added and the moist dust pelletized. The prepared material is charged on 
to the sinter bed by means of a spout which swings from side to side across the 
width of the grate, thus eliminating the tendency for the larger pellets to run to the 
edge. The sintered material, after cooling, is ground in roller mills. 


" China Clay as a Sewage Filter." Anon. Chem. Age, 1924, 11, 92. 

" China Clay as a Reinforcing Agent in Rubber Compounding." By T. J. Drakeley and W. F. O. 

Pollett. Trans. Inst. Rubber Ind., 1928-9, 4, 423-60. 
" Grit in China Clay." By J. Strachan. Worlds Paper Tr. Rev. 1930, 93, 482-6. 
" China Clay (Kaolin)." Anon. Min. Indus, of Br. Empire and Foreign Countries, Imperial 

Institute (Lond.), 1931, 100 pp., including bibliography. 
" Economic and Manufacturing Aspects of the Building Brick Industries." By A. Zaiman and 

W. A. Maclntyre. Building Res. Station, H.M.S.O., London, Special Rep. No. 20, 1933, pp. 

" Refractory Materials, Their Manufacture and Use." By A. B. Searle. 3rd Ed., London, 1940. 
" Syllabus of Clay Testing. (Part I)." By T. A. Klinefelter, R. G. O'Meara, S. Gottlieb and G. L. 

Truesdell. U.S. Bur. Mines Bull. No. 451, 1943, 35 pp. (Includes survey of tests, uses for 

particular types, and bibliography.) 
" The Report of a Working Party on China Clay." Bd of Trade. C.M.D. 6/48, 1946, 14 pp. 
" China Clay or Kaolin." War Changes in Industry Series, U.S. Tariff Comm. Rep. No. 23, 1947, 

75 pp. 
" Bricks and Modern Research." By B. Butterworth. London, 1948, pp. 895. 
" The Production of Lightweight Concrete Aggregates from Clays, Shales and other Materials." 

By J. E. Conley et al. U.S. Bur. Mines Rep. Invest., 4401, 1948, 121 pp. 



"Basic Refractories; Their Chemistry and their Performance." By J. R. Rait. London, 1950, 

408 pp. (219 biblio. refs.) „ „ . „ „ „ ,, 

'* Clay Building Bricks of the United Kingdom." By D. G. R. Bonnell and B. Butterworth. 

Ministry of Works, National Brick Advisory Council Paper, No. 5. ,„«, „ 

" St. Austell China Clay Industry." By L. A. Stuttridge. Camborne Sch. Mm. Mag., 1951 (June), 

" Clay and Clay Products." By R. B. Lodoo and W. M. Myers. " Non-Metallic Minerals," New 

York, 1951, 2nd ed., pp. 141-164. , 

" Production Methods in the Scottish Firebrick Industry." By J. McWilham. Refrac. J., 1952, 

No. 3, 97-109. , „ „ „ . _ „ 

" The Heavy Clay Industries." By W. Noble. In " Ceramics, A Symposium, Brit. Ceram. Soc, 

Stoke-on-Trent, 1953, pp. 738-770. „-„, «,,, /t i -,-,<> <■ -v 

" Properties of Clay Building Materials." By B. Butterworth. ibid., pp. 824-877 (Incl. 278 refs.). 
" Devon Ball Clays and China Clay." By H. W. Webb; Watts, Blake, Bearne & Co., Newton 

" Requirements of Modern Paper Clay." By C. G. Albert. Min. Eng., 1955, 7, No. 10, 941-43. 
" The Production of Lightweight Aggregate by the Sinter-Hearth Process. By F. Catchpole. 

Trans. Brit. Ceram. Soc, 1957, 56, No. 10 519-528. 
" Some Aspects of Ceramics in Atomic Energy." By P. Murray. Refrac. J., 1957, 33, No. 1, 2-6. 
" Standardized China Clay for the Pottery Industry." By N. O. Clark. Trans. Brit. Ceram. Soc, 

" Scientific Grouping of South Devon Ball Clays." By V. R. G. Ashcroft-Hawley. Watts, Blake, 

Bearne & Co. Ltd., Newton Abbot, 1958, 27 pp. 
" Composition Variation in Ball Clays." By H. A. Holdndge. Trans. Brit. Ceram. Soc, 1959, 

" The Chemistry' and Physics of Clays." By A. B. Searle and R. W. Grimshaw. 3rd Ed., London, 

1959 942 pp. 
" Clay " By H. H. Murray." Industrial Minerals and Rocks," ed. by J. L. Gillson. Amer. Inst. 

Min. Met. and Petrol. Engnrs., 3rd ed., I960, pp. 259-284. „ „ „* ,„*„,,. 

" Clays." By T. de Polo. " Mineral Facts and Problems," U.S. Bur. Mines Bull. 585, 1960, 14 pp. 
" The Scientific Grouping of Ball Clays." Watts, Blake, Bearne & Co. Ltd., Newton Abbot. 6 pp. 
" Molochite " Technical Handbook, English Clays, Lovering, Pochm & Co., St. Austell, 

England, 24 pp. 
" Clays." U.S. Bur. Mines. Minerals Yearbook, (Annual). 


American Society for Testing Materials 

A.S.T.M. Standards 1958: 

Aluminium Silicate Pigments. D 603-42. 

Fireclay and High Alumina Refractory Bricks. C 27-58. 

Building Bricks. C 62-44. 

British Standards Institution: 

Extenders for Paints. B.S. 1795 : 1952. 
Kaolin for Aircraft Purposes. M 21 : 1947. 
China Clay (Kaolin). M.A.P.— D.T.D. 374. 
Clay Engineering Bricks. B.S. 1301 : 1946. 
Hollow Clay Building Bricks. B.S. 1190 : 1944. 
Clay Tiles for Flooring. B.S. 1286 : 1945. 
Clay Roofing Tiles. B.S. 402 : 1940. 


Cobalt compounds are found fairly widely distributed in nature, but they usually 
constitute only a small percentage of the lode in which they occur. It has been 
estimated that the quantity of cobalt in the earth's crust amounts to about only one- 
quarter of that of nickel. No deposits are worked solely for their cobalt content, 
the metal being usually obtained as a by-product in the extraction of other metals, 
particularly copper, nickel and gold. A large number of cobalt minerals have been 



described, but, from the commercial standpoint, the most important are arsenides, 
sulphides, and oxides. Frequently, the arsenides are associated with nickel, 
gold and silver, whilst the sulphides often occur with copper ores. 

The principal cobalt sulphide minerals are carrollite (Q1S.C02S3), and linnaeite 
(C03S4); the chief arsenides being smaltite (CoAs 2 ), cobaltite (CoAsS) and skutteru- 
dite (C0AS3). Oxidized cobalt ores include asbolite, a mixture of cobalt and man- 
ganese oxides in which the cobalt may vary from 4 to 30 per cent., and heterogenite, 
a hydrated cobalt oxide which sometimes contains copper, nickel and iron. 

The chief types of cobalt ore worked commercially are: (1) the Canadian silver- 
cobalt arsenide ores; (2) copper-cobalt sulphide ores produced in Northern 
Rhodesia by the Rhokana Corporation Ltd., and by the Rhodesian Selection 
Trust. As fed to the concentrator the ores produced by the Rhokana Corporation 
contain the following percentages: copper, 3; cobalt, 014; iron, 2-5; sulphur, 1 -5; 
silica, 45; alumina, 12; magnesia, 7; lime, 7; (3) copper-cobalt oxidized ores 
produced by the Union Miniere du Haut Katanga; (4) chalcopyrite-cobaltite 
containing 0-4-10 per cent, cobalt produced in Idaho, U.S.A.; (5) copper-lead- 
cobalt-nickel sulphide ores, such as those mined in Madison Co., Missouri, which 
contain the following percentages: cobalt, 0-87; nickel, 108; lead, 1-28; copper, 

World Production 

The world's production of cobalt ore has risen very considerably in recent years 
and in 1958 the recorded outputs (in terms of metal content) totalled 14,000 long 
tons, excluding that contained in complex ores mined in Finland, Greece, Norway, 
Spain, Sweden, China and Korea. The countries recording the largest outputs were 
the Belgian Congo, the United States, Northern Rhodesia, Canada, Uganda and 
Morocco. The countries recording productions of metallic cobalt were the Belgian 
Congo, the United States, Northern Rhodesia, Federal Germany, France and 
Norway. Cobalt and its compounds are known to be produced in the United 
Kingdom, Canada, Belgium and the U.S.S.R. Federal Germany extracts cobalt 
mainly from pyrites sinter imported from Finland, Norway and Sweden. United 
Kingdom imports of cobalt in the form of rondelles, pellets and squares in 1958 
totalled 707 long tons, and of cobalt oxide 317 long tons. The largest importer of 
cobalt is the United States which in 1957 imported ore containing 372 long tons of 
cobalt, 7,220 long tons of cobalt metal, 289 long tons of cobalt oxide and 163 long 
tons of cobalt salts. In 1958 they imported 7,017 long tons of cobalt metal, 374 long 
tons of cobalt oxide and 105 long tons of cobalt salts. 

In Canada, cobalt is obtained principally as a by-product of nickel production 
from the nickel-copper ores extensively mined in the Sudbury District of Ontario. 
Other sources are the nickel-copper ores mined in the Lynn Lake district of Mani- 
toba and the cobalt-silver ores produced in the Cobalt-Gowganda area of North- 
eastern Ontario. The International Nickel Co. of Canada Ltd. produce electrolytic 
cobalt at their refinery at Port Colborne, Ontario. Falconbridge Nickel Mines Ltd. 
recover cobalt from ores raised in the Sudbury district, and the Sherritt Gordon 
Mines Ltd. extract cobalt from ore mined at Lynn Lake, Manitoba. 



In Morocco the cobalt occurs, with gold, nickel, and silver, as smaltite, 
skutterudite and safflorite, in deposits which lie in a desert region near Bou-Azzer. 

Extraction of Cobalt 

The world's supply of cobalt is obtained in connection with the smelting or 
refining of other metals of diverse modes of occurrence and processes for recovering 
cobalt, or its compounds, in marketable form naturally vary considerably. It will 
therefore only be possible to outline here the methods used at the two largest 
producing centres, in the Belgian Congo and Northern Rhodesia. 

In the Belgian Congo cobalt-bearing ore is obtained mostly from deposits near 
Elisabethville and Jadotville where the metal occurs chiefly as oxidized compounds. 
Most of the recovery is made from the treatment of copper concentrates which 
carry from 6 to 14 per cent, of cobalt. The concentrates are smelted in an electric 
furnace so as to yield two separable alloys (termed " white " and " red ") and a 
cobalt-bearing slag. The white alloy, the lighter of the two, which contains about 
42 per cent, cobalt, 15 per cent, copper, 39 per cent, iron and 1-2 per cent, silicon, is 
cast into ingots and exported for refining at Oolen, Belgium. 

The red alloy, which contains about 4-5 per cent, cobalt and 89 per cent, copper, is 
refined locally for its copper, the resultant slag, which carries about 1 5 per cent, cobalt, 
being returned with a new charge of ore to the electric furnace. An electrolytic plant 
for treating the slime residues from the copper plant is in operation at Jadotville. 

In Northern Rhodesia cobalt occurs principally associated with copper ores as 
the sulphide, carrollite, but part may be present as oxidized ores, such as asbolite. 
It is not evenly distributed throughout the copper sulphide ore and may vary from a 
trace up to 3 per cent., the average cobalt content of ore sent to the Rhokana smelter 
being 17 per cent, with about 26 per cent, copper. Practically all the ore treated 
for cobalt at the smelter is obtained from the Nkana mine. 

By selective flotation, the ore is concentrated and separated into two products, 
one carrying 32 per cent, copper and 0-8 per cent, cobalt, and a second carrying 17 
per cent, copper and 2-8 per cent, cobalt. The concentrates are smelted separately in 
reverberatory furnaces with charges adjusted so that most of the cobalt passes to the 
slag, which is next smelted in an electric furnace to produce an alloy containing 
about 37 per cent, cobalt, 47 per cent, iron, 14 per cent, copper and 1 per cent, 
sulphur. The alloy, after being granulated, is exported. 

Processes for obtaining commercially pure cobalt, or its oxides, from the cobalt- 
iron-copper alloy are much the same at Oolen, Belgium ; Deloro, Ontario, Canada, 
and Clydach, S. Wales. Before World War II part of the cobalt alloy exported from 
the Belgian Congo and Northern Rhodesia was refined at the Lemathe refinery in 
Westphalia, Germany and part in Belgium. 

The typical chemical compositions of cobalt compounds marketed by the Mond 
Nickel Co. Ltd., which has a plant at Clydach, S. Wales, are shown in Table 52. 

Before World War II the sale of the principal production of cobalt and its alloys 
was closely controlled by the International Cobalt Association. There also existed a 
Cobalt Oxide Convention which controlled the sales of cobalt oxide and salts. 
Neither organization has been revived. 



Table 52 

Analyses of Cobalt Oxides and Salts. 
Per Cent. 















6H a O 


Cobalt, Co 







Nickel, Ni 







Copper, Cu 







Lead, Pb . 







Iron, Fe . 







Lime, CaO 







Magnesia, MgO 







Soda, NaaO 







Sulphur, S 







Silica, Si0 2 







The Cobalt Information Centre, the executive organisation of the Cobalt 
Development Institute, was set up in Brussels in 1957, with a branch office in Ohio. 


The consumption of cobalt by industries in the United States, the world's largest 
user, is shown in Table 53, from which it will be seen that, with the return to peace- 
time conditions, the demand for cobalt for use in cemented carbide tools and 
" Stellite " alloys decreased, but the quantity used for magnets and for enamelling 
metal shows a considerable increase. 

It has been estimated that of the cobalt oxide and salts imported into Great 
Britain, about 52 per cent, is used by the ceramic industry, 27 per cent, by chemical 
industry for the manufacture of salts, whilst pigments and other uses account for 
21 per cent. 

Metallic cobalt, when pure, melts at 1,480° C. and boils at about 2,900° C. After 
iron it is the most magnetic of the metals and it retains this characteristic up to a 
temperature of about 1,150° C. Its specific gravity is 8-76 when in the cast form and 
8-81 when annealed. The Brinell hardness varies with treatment and ranges from 
about 124 to 130 for the cast metal and up to 270 or 310 for electrodeposited metal. 
Cobalt can be cast, annealed, rolled, machined or drawn into wire. 

Ferrous Alloys. Cobalt alloys readily with iron to give malleable and weldable 
products and the metal is an important constituent of many high-speed tool steels, 
being added to improve their cutting efficiency at high temperatures. Iron-cobalt 
alloys are most useful for permanent magnets on account of the high value for flux 
densities which can be obtained with medium magnetizing forces. Such magnet steels 
in commercial production usually also contain other metals. A typical permanent 
magnet steel would contain about 35 per cent, cobalt, 4 per cent, tungsten, 2 per 
cent, chromium, 57 per cent, iron and 09 per cent, carbon. " Alnico " magnets 
carry from 5 to 35 per cent, cobalt, 14 to 30 per cent, nickel, 6 to 12 per cent, 
aluminium, and the remainder iron. 



Table 53 

Cobalt consumed in the U.S.A.* (1,000 lb. of contained cobalt) 








High-speed steel .... 






Other steel 






Permanent alloy magnets . 






Soft magnetic alloys 






Cobalt - Chromium - Tungsten - 

Molybdenum alloys: 

Cutting and wear-resisting materials 






High temperature, high strength 







Alloy hard-facing rods . 






Cemented carbides .... 






Other metallic .... 






Total Metallic 






Non-metallic (exclusive of salts and 
Ground coat-frit .... 












Other non-metallic .... 






Total Non-metallic .... 






Salts and driers, lacquers, varnishes, 

paints, inks, pigments, enamels, 

glazes, electroplating, etc. (estimated) 






Grand Total 






* Adapted from " Minerals Yearbook," 17.5. Bur. Mines. 

The U.S. National Stockpile Specification P-13R, dated March 10th, 1953, for 
the purchase of metallic cobalt for use in ferrous and non-ferrous alloys, requires a 
mini m um of 97 per cent, of cobalt, with the following limits for impurities: nickel, 
0-75 per cent.; iron, 0-3 per cent.; carbon, 0-5 per cent.; copper, 01 per cent.; 
sulphur, 005 per cent. ; phosphorus, 002 per cent. 

Non-Ferrous Alloys. The most important of the non-ferrous cobalt alloys is the 
group known as the " Stellites," which consist essentially of alloys of chromium, 
tungsten and cobalt, with possibly molybdenum, iron and nickel. They are charac- 
terized principally by their resistance to corrosion and abrasion, hardness and ability 
to take high polish. These properties make them of value in many types of chemical 
plant. The " Stellites " are chiefly employed as cutting tools, and for many purposes 
where freedom from oxidation and distortion at high temperatures is essential, such 
as in the exhaust valves of aircraft motors, the exhaust ports of marine diesel engines, 
turbo-supercharger blades and jet buckets. 

The composition of commercial cobalt alloys of this type varies considerably, 
and the cobalt content may range between 45 and 65 per cent. 



Metallic Cobalt. One of the most important uses for metallic cobalt, apart from 
its employment in alloys, is as a binding material in the manufacture of cemented 
tungsten carbide and tantalum carbide tools. For this purpose from 3 to 15 per cent, 
of cobalt powder is intimately mixed with the carbide and the whole heated to about 
1,375° C. About 5 or 6 per cent, of cobalt is used to sinter tools intended for cutting 
steels, non-ferrous alloys, ceramic materials, glass and plastics. When the tool is 
intended for extra heavy wear, such as in mining drills or for rough shaping hard 
steels, the cobalt content may vary between 8 and 14 per cent. Cobalt is also used as 
a binder for diamond or diamond dust in cutting tools. 

Cobalt Plating. As the metal oxidizes rather more readily than either nickel or 
chromium, it is not extensively used for electroplating. Small quantities of a cobalt 
salt up to about 0-3 per cent, are, however, often added to nickel-plating solutions. 

Ceramic Uses. Probably the greater proportion of the cobalt used in ceramics is 
employed in the manufacture of whiteware, wall tiles, and sanitary ware in order to 
neutralize the yellowish colour due to small amounts of iron in the raw materials. 
The quantity used, however, rarely exceeds the equivalent of 1 lb. of oxide per ton of 
ware. Cobalt, in the form of its grey oxide, silicate or aluminate, is sometimes used 
to give a blue colour to pottery, enamels and glazes. In the trade, the silicate colour 
is usually known as mazarine or royal blue, while the aluminate is termed Thenard's 
blue or matte. These blues can be widely modified by the addition of other metallic 
oxides so as to produce types known as Willow, Canton, Peacock, Unique, Mulberry, 
Violet and Black. The colours produced are stable at high temperatures and un- 
affected by oxidizing or reducing atmospheres or by silicates. The cobalt may be used 
in the form of Thenard's blue, a compound produced by heating a mixture of cobalt 
oxide and ammonia alum. Cobalt oxide is an essential component of all black 
ceramic colours, except iridium black. Such colours often also contain nickel, 
chromium and manganese oxides. In the vitreous enamelling of metals, cobalt 
plays an important part in ground coat enamels for iron vessels as it increases the 
adhesion of the enamel to the metal. The quantity used is about 0-5 per cent, of the 
enamel mixture, the cobalt being often added in the form of an alkali silicate. 

Recently, cobalt has been used for facilitating the joining of metal and ceramic 

Glassmaking. Cobalt may be added to the batch for two purposes : (a) to produce 
a deep blue glass; about 18 oz. of cobalt oxide being used to each ton of glass: 
(b) in amounts of a few grams per ton to neutralize yellowish tints due to the 
presence of iron or selenium. 

Cobalt Catalysts. The most common use for cobalt in this connection is as a 
drier for accelerating the oxidation of vegetable oils in paints. The compounds used 
are the borate, acetate, carbonate, sulphate, resinate, linoleate and naphthenate. 

Metallic cobalt is an important constituent of the catalyst used in the Fischer- 
Tropsch process for synthesizing petrol from coal. This type of catalyst was em- 
ployed commercially in Germany before and during World War II. It is highly 
selective for the synthesis of hydrocarbons from hydrogen and carbon monoxide. 
However, this catalyst has now been almost entirely replaced by a similar, iron- 
containing material, since it is cheaper, and by its use it is easier to control the 



process. Cobalt is also an important constituent in the cobalt-molybdenum oxide 
catalyst employed for the removal of certain organic sulphur compounds from 
mineral oils. The oxides, which are supported on alumina, are exposed to such oils 
at elevated temperatures and pressures in the presence of a flow of hydrogen. In use 
they rapidly become sulphided, but nevertheless remain extremely active and select- 
ive agents for the conversion of compounds of the thiophene type to hydrocarbons 
and hydrogen sulphide. The hydrogen sulphide may then be easily separated. 
Catalysts of this type are employed throughout the world. 

Cobalt fluoride has been used as a fluorinating agent in connection with the 
synthesis of fluocarbon compounds which are finding use in the separation of 
uranium isotopes and for other purposes (see p. 199). 

Cobalt in Animal Nutrition. In many parts of the world, due to soil conditions, 
grazing animals are deficient in cobalt. Cobalt is essential to the life of the animal 
organism for in vivo it is incorporated into the important factor, vitamin B. 12. 
This cobalt deficiency may be rectified by the administration of cobalt in the form 
of a simple salt. In certain circumstances it is also attractive to administer the 
cobalt in the form of a cemented cobalt oxide pellet, which is carried in the rumen 
of the animal throughout its life. Vitamin B. 12 itself is also widely employed to 
treat certain pathological conditions in human beings, in particular pernicious 


" Cobalt: Its Occurrence, Metallurgy, Uses and Alloys." By C. W. Drury. Canad., Ontario Bur. 

Mines, 1918, 27, Pt. Ill, Section 1, 133 pp. 
" Cobalt Ores." By E. Halse. Monographs on Min. Res. with Special Ref. to the Br. Empire, 

Imperial Institute, 1920, 54 pp., including bibliography. 
" Coloured Glasses: A Monograph prepared for the Society of Glass Technology." By W. A. 

Weyl. Pt. IV, /. Soc. Glass Tech., 1944, 28, 158-266. (Cobalt, 203-31.) 
" Le Cobalt." By R. Perrault. Paris, 1946, 151 pp., including bibliography. 
*' Cobalt." By R. S. Young. London, 1948, 181 pp. 
" Electrowinning of Cobalt from Cobaltite Concentrates." By F. K. Shelton, J. C. Stahl, and R. 

E. Churchward. U.S. Bur. Mines, Rep. Invest. No. 4172, 1948, 98 pp. 
" The Metallurgy of Cobalt." By W. H. Dennis. Mining Mag. (Lond.), 1949, 81, 144-6 and 215-8. 
" Cobalt Refining at Rainham Works of Murex Ltd." By P. S. Bryant. " The Refining of Non- 
ferrous Metals." Inst. Min. Met., 1949, pp. 259-73. 
' ' Cobalt : Sources, Uses, Limitations and Future Supply Possibilities." By the Staff of the Journal 

of Metals. /. Metals, 1951, 151 (Jan. Sect. 1), 17-24. 
" The Cobalt Enigma." By W. von Haker. Chemische Industrie, 1957 (Dec.), 129-134. 
" Cobalt." By Paul Job, in " Nouveau Traite de Chimie Min6rale." Ed. by P. Pascal. Paris, 1959, 

Vol. XVIII, pp. 413-760. 
" Cobalt." By J. H. Bilbrey, Jnr. " Mineral Facts and Problems." U.S. Bur. Mines Bull. 585, 

1960, 12 pp. 
" Description of Nickel-Cobalt Operations." By the Staff of Falconbridge Nickel Mines Ltd. 

Canad. Min. Jour., 1959, June, 177-230. 
" Cobalt and Nickel in the Vitreous Enamelling Industry." By J. E. Hansey. The Mond Nickel 

Co. Ltd. Lond., 12 pp., including bibliography. 
" The Use of Cobalt and Other Metals as Driers in the Paint and Allied Industries." By J. H. 

Morgan. The Mond Nickel Co. Ltd. Lond., 20 pp., including bibliography. 
" Cobalt in Animal Nutrition." By A Fraser. The Mond Nickel Co. Ltd. Lond., 15 pp. 
" Cobalt, Nickel and Selenium in Pottery." By H. W. Webb. The Mond Nickel Co. Ltd., Lond. 
'* Cobalt." Information Centra, Brussels (Quarterly). 
" Cobalt." U.S. Bur. Mines. Minerals Yearbook (Annual). 


U.S. National Stockpile Specification 

Metallic Cobalt (for use in ferrous and non-ferrous alloys. P-13R, March 10th, 1953. 



Copper is found in nature both as the metal and in combination as the sulphide, 
carbonate and oxide. In all, between two and three hundred copper-bearing minerals 
have been described in the literature. 

The most commonly occurring copper minerals are the sulphides, chalcocite 
(Q12S), chalcopyrite (Cu.FeS2>, covelline (CuS) and bornite (CusFeS^: the oxide, 
cuprite (CuaO): the carbonates, malachite and azurite: the silicate, chrysocolla and 
native copper. 

Copper deposits are found in igneous, sedimentary and metamorphic rocks. As 
all copper minerals are attacked by natural weathering agencies, copper deposits are 
liable to oxidation and leaching near the surface and redeposition of the copper in 
another form at lower levels. 

The average percentage of copper in an ore as mined, which will make its 
working a remunerative proposition, depends upon the nature of the occurrence 
but where very large tonnages can be handled daily, ores carrying as little as 1 per 
cent, may be workable at a profit. The average grade of copper ore worked in the 
three leading producing countries is about 1 per cent, in the United States, 2 per cent, 
in Chile, and 3 per cent, in Northern Rhodesia. 

It is interesting to note that the large deposits of disseminated copper sulphide 
ores worked in the Belgian Congo are estimated to contain about 80 million tons 
of ore averaging about 6-4 per cent, of copper, whilst those adjoining in Northern 
Rhodesia are estimated to contain 450 million tons, averaging 3-9 per cent, of 
copper. The two fields together in 1957 produced over 650,000 long tons of copper. 

Most copper ore as mined needs concentration before it can be smelted economi- 
cally. The treatment naturally varies with the nature of the ore and the associated 
minerals; in general, however, treatment of copper sulphide ore consists of crushing, 
grinding, sizing and then concentrating by flotation. In the case of ores carrying the 
copper both as sulphides and oxides, a further flotation treatment may be required 
to recover the oxides. The concentrates obtained from sulphide ores may contain 
50-55 per cent, of copper and represent a recovery of over 90 per cent, of the copper 
present in the ore. The recovery of copper present as oxide is often rather lower. 
Copper silicate ore presents special problems, as it is difficult, if not impossible, to 
float and the copper cannot be leached out by acids. 

World Production 

The world's production of copper ore has been steadily rising for some years 
past. In 1949 the estimated copper content of ore mined was 2,260,000 long tons, 
and this had risen to 3,400,000 long tons by 1958. Of the latter amount the con- 
tribution from British countries was equal to 922,000 long tons of copper. The 
world's metal production of copper from ore totalled 3,400,000 long tons in 1958 
and of this 791,309 long tons was produced in British countries (Northern Rhodesia, 
Canada, Australia, the Union of South Africa, India and Uganda). 

For many years past Great Britain has produced only negligible amounts of 



copper ore, her large consumption of copper being met by imports of the metal, 
which in 1958 comprised chiefly 308,128 long tons of electrolytic bars, ingots, etc., 
5 1 ,370 long tons of other refined copper and 95,878 long tons of blister copper. 

The recovery of secondary copper is an important industry in certain consuming 
countries. Thus, the United States between 1952 and 1957 recovered amounts 
varying between 736,000 and 882,000 long tons per annum. 

Metallurgy of Copper 

Numerous methods have been used for obtaining metallic copper from its ores, 
depending upon the nature of the ores and local conditions. It must suffice here to 
indicate briefly one method of smelting finely divided concentrates carrying copper 

The concentrates are roasted to expel some of the sulphur as sulphur dioxide, 
and then smelted on a reverberatory hearth so that all the copper forms cuprous 
sulphide and the remainder of the sulphur combines with the iron to form ferrous 
sulphide, the excess of iron going to the slag. The copper and iron sulphides fuse 
together to form a " matte," which is tapped off and then blown in a converter, 
whereby the iron sulphide is oxidized and combines with silica to form slag. The 
copper sulphide undergoes various reactions, with the final production of metallic 
(" blister ") copper and sulphur dioxide. 

The impurities present in blister copper depend upon the composition of the ore 
from which it was obtained. It may, therefore, contain precious metals, lead, 
bismuth, antimony, arsenic, selenium, tellurium, nickel and cobalt, most of which 
have a deleterious effect on the electrical conductivity or working properties of 

The refining processes to be adopted vary with the quantity and nature of these 
impurities and are too complicated to be described here in detail, and reference 
should be made to the comprehensive papers on the Fire Refining and Electrolytic 
Refining of Copper in the Symposium on the Refining of Non-ferrous Metals, 
published by the Institution of Mining and Metallurgy in 1950. 

Most commonly, the blister copper is cast into anodes and refined electrolytically, 
and the cathode copper so obtained is then further purified by fire refining. Only a 
few deposits yield blister copper of a composition which permits of its being fire- 
refined direct with the most economical results. 

Typical analyses of anode copper, electrolytically refined cathode copper and 
R.E.C. brand electrolytic copper produced at the Nkana refinery are shown in 
Table 54. 

It has been estimated that of the total quantity of primary copper marketed 
annually, about 74 per cent, is probably obtained by the melting electrolytically 
prepared cathodes and about 14-8 per cent, by the fire-refining of blister copper. 
Cathode copper used for alloying purposes without refining constitutes about 5-4 
per cent, and an additional 5-8 per cent, is melted and cast without further refining. 

The slimes which remain in the anode compartment in the electrolytic refining 
of copper usually constitute a valuable source of a number of the less common 
elements such as selenium, tellurium, and bismuth. Thus the slimes produced at the 



Table 54 

Analyses of Copper Produced at the Nkana Refinery 


Anode Copper 

Refined Cathode 

R.E.C. Brand 
Electrolytic Copper 

Per cent. 

Per cent. 

Per cent. 

Copper .... 








Cobalt . 




Nickel . 








Arsenic . 




















Oxygen . 








Nkana refinery in Northern Rhodesia which amount, after drying, to about 14 
per cent, of the weight of anodes consumed contain about 12 oz. of gold and 
1,287 oz. of silver per ton, with copper 43-55 per cent.; selenium, 12-64 per cent.; 
tellurium, 106 per cent.; bismuth, 1 17 per cent.; with smaller amounts of nickel, 
cobalt, lead and antimony. 

A number of types of raw copper are marketed, each differing somewhat from 
the others and having its own particular field of utility. The chief characteristics of 
these types are summarized below. 

1 . Cathode Copper. This is obtained by the electrolytic refining of blister copper 
and is the raw material for the production of electrolytic high conductivity copper 
(both tough-pitch and oxygen-free) and is used for making special alloys with silver, 
cadmium or chromium where low specific resistance is of primary importance. Such 
copper is dealt with in British Standard Specification B.S. 1035 : 1952. 

2. Tough-pitch high conductivity {H.C.) copper, which contains 99-9 per cent, or 
more copper, is extensively used for electrical purposes and where high thermal 
conductivity is particularly important. 

3. Tough-pitch Copper. Several grades of this type of copper are marketed, 
usually containing up to 0-5 per cent, of other elements, which prevent the copper 
from conforming to the conductivity standard for H.C. copper. 

4. Tough-pitch Arsenical Copper. This product contains 0-3-0-5 per cent, of 
arsenic which gives slightly increased strength at ordinary temperatures and raises 
by about 100° C. the temperature at which softening first occurs upon annealing. 
Arsenical copper has a somewhat better resistance to oxidation at moderate 
temperatures than has ordinary copper. Its electrical conductivity is only about 
half that of pure copper. This type is covered by B.S. 1173 : 1952. 

5. Deoxidized Copper. Tough-pitch copper usually contains from 0-02 to 0-10 
per cent, of oxygen, and although this element has very little effect on the physical 
and mechanical properties of the metal, it is objectionable in copper which is to be 



welded, as its interaction with the hydrogen in the welding gases may give steam, 
causing unsoundness in the weld. To overcome this objection various grades of 
deoxidized copper are marketed and used, particularly for plant construction. 

Deoxidized copper is covered by British Standard Specification No. 1172 for 
" Phosphorus deoxidized non-arsenical copper," and No. 1174 for " Phosphorus 
deoxidized arsenical copper." In both cases, the residual phosphorus lowers the 
thermal and electrical conductivities of the metal, so that for the non-arsenical type 
they are from 70 to 90 per cent, of the values for pure copper, whilst for the arsenical 
type they are from 25 to 40 per cent. 

The British Standards Institution's Specification for Oxygen-free High Conduc- 
tivity Copper requires the product to contain not less than 99-95 per cent, copper 
(silver being counted as copper); bismuth, not exceeding 001 per cent.; lead, not 
exceeding 005 per cent., and the total of all impurities (excluding silver) is limited 
to 003 per cent. 

A.S.T.M. Specification No. B 170-47 covers wire bars, billets, and cakes of 
oxygen-free electrolytic copper produced without the use of residual metallic or 
metalloidal de-oxidizers. The copper in all shapes shall have a minimum purity of 
99-92 per cent., silver being counted as copper. By agreement between the manu- 
facturer and the purchaser the addition of silver up to 30 oz. per ton will be con- 
sidered to be within the specification; silver being counted as copper in the chemical 
analysis. The copper in all shapes shall have a resistivity not to exceed 015328 
ohm (metre, gram) at 20°C. (annealed). " Resistivity " is used in place of " con- 
ductivity." The value of 015328 ohm (metre, gram) at 20°C. is the International 
Annealed Copper Standard for the resistivity of annealed copper equal to 100 per 
cent, conductivity. 

The British Standards Institution has issued two sets of specifications for Raw 
Copper (B.S. 1035-1040), and for Deoxidized and Arsenical and Non-Arsenical 
Coppers (B.S. 1172-1174); all dated 1952. 

As regards chemical composition, No. 1035 for Cathode Copper and No. 1036 
for Electrolytic Tough-Pitch (i.e. oxygen bearing) High Conductivity Copper, both 
require the products to contain not less than 99-90 per cent, of copper (silver being 
counted as copper) with the following limits for impurities : bismuth, 001 per cent. ; 
lead, 0-005 per cent. ; total of metallic impurities, excluding silver, 03 per cent. In 
the case of No. 1036, total impurities also exclude oxygen. 

Tough-pitch coppers, containing 99-85 per cent., 99-75 per cent, and 99-50 per 
cent, of the metal, not intended for electrical purposes and of which the conductivity 
is not specified, are dealt with in B.S.I, specifications 1038, 1039 and 1040. The 
requirements in regard to chemical composition are summarized in Table 55. 
Similar details from A.S.T.M. specification B 72-55T for fire refined casting 
copper for cast alloys and B 216-49 for fire-refined copper for wrought products 
and alloys are shown in Table 56. 

The U.S. National Stockpile Specification P-16-R3, of August 10th, 1956, lists 
five types of copper each to conform to certain chemical and physical requirements, 
as follows: 

(«) Electrolytic cathode copper shall conform to the requirements of A.S.T.M. 



Table 55 
B.S.I. Specifications for Copper {other than High Conductivity Grades) 

Copper (silver counted as 
copper), min. 

Antimony, max. 

Arsenic, max. 

Bismuth, max. 

Iron, max. . 

Lead, max. . 

Nickel, max. 


Selenium, max. 

Tellurium, max. 

Tin, max. 

Oxygen, max. 

Total of all impurities 
excluding nickel, oxy- 
gen and silver . 

1038 : 1952 

99-85 per 





1039 : 1952 

99-75 per 





1040 : 1952 

99-50 per 






1073 : 1952 





1074 : 1952 









05 1 














* For copper to withstand severe working conditions between 400-700° C, the 
limit for bismuth is 0-0015 per cent. 

t Not less than 0-015 per cent. 

t Selenium plus tellurium. 

§ Excluding nickel, silver, arsenic and phosphorus. 

II Arsenic not less than 0-30 per cent. 
** By agreement between purchaser and manufacturer, the bismuth content may 
be increased beyond these limits. 

Table 56 

Some A.S.T.M. Specifications for Copper 

B 216-49 

Fire Refined 

Copper for Wrought 

Products and Alloys 

B 72-55T 

Fire Refined Casting Copper 

for Cast Alloys 

Grade A 

Grade B 

Per cent. 

Per cent. 

Per cent. 

Copper plus Silver, Cu + Ag, min. 




Arsenic, As, max. 




Antimony, Sb, max. 




Bismuth, Bi max 




Iron, Fe, max. . 




Lead, Pb, max. . 




Nickel, Ni, max. 




Oxygen, O, max. 




Selenium, Se, max. 

\ 0025 



Tellurium, Te, max. 



Sulphur, S, max. 




Tin, Sn, max. 






B 115, latest revision. Cathodes may be of any size usual with the producer. All 
cathodes supplied under any contract shall be of the same nominal size. 

(b) Electrolytic copper wire bars shall conform to the requirements of A.S.T.M. 
B 5, latest revision, and shall be in the form of 250 lb. wire bars. 

(c) Lake copper ingot bars (low resistance) shall conform to the requirements of 
A.S.T.M. B 4, latest revision, and shall be in the form of 50 lb. ingot bars. 

(d) Fire refined copper for wrought products and alloys shall conform to the 
requirements of A.S.T.M. B 216, latest revision, and shall be in the form of 50 lb. 
ingot bars. 

(e) Oxygen-free electrolytic copper (OFHC Brand) shall be Certified Grade and 
shall conform to the following requirements: 

Chemical composition Per cent, by weight 

Copper + silver, min. . . . . . .99-96 

Phosphorus, max. 0003 

Sulphur, max 0040 

Zinc, max. 00003 

Mercury, max. ....... 0-0001 

Lead, max. 00010 

Sizes : All wire bars shall be 4 in. x 4 in. X 54 in. ; billets shall be 3 in., 6 in., 7in. or 
8 in. in diameter; and all cakes shall be 4 in. x 13 in. x 52 in. 

Electrical conductivity: 100 per cent. I.A.C.S. minimum. Density: 8-90 gms./c.c. 
minimum. Finish on surfaces : Limitation on amount of chipping — no more than one 
chip for each 2 ft. of cast length. Embrittlement Testing: number of 90° bends on 
hydrogen-annealed test wires— a minimum of ten bends. Microscopic examination 
for presence of cuprous oxide: There shall be no cuprous oxide visible at a magni- 
fication of 200 diameters. 


The main properties which give metallic copper its chief industrial importance 
are high electrical and thermal conductivities, high ductility (which enables it to be 
shaped at ordinary temperatures), moderate tensile strength, ability to form many 
useful alloys with other metals, and resistance to attack by many chemicals, except 
strong mineral acids and ammonia. 

Some copper compounds are of importance in agriculture owing to their fungi- 
cidal properties and others are valuable in paints. 


Copper has the highest electrical conductivity of any metal except silver. 
According to the International Copper Standard, the specific resistance of pure 
annealed copper at 20° C. is 1 -7241 microhms-cm. Hence its conductivity is 0-58001 
reciprocal microhm-cm. The conductivity of any sample of copper is often 
quoted as a percentage of this amount. In the fully annealed condition, modern high 
conductivity copper often has a conductivity of 101 or 102 per cent. 



The physical properties of copper are modified considerably by the presence of 
small percentages of certain other elements. Thus, its electrical conductivity is 
decreased by most other elements except silver, zinc, lead and cadmium. 

Copper in Chemical Plant. Copper is widely used in many types of chemical 
plant, either as the metal or in the form of its alloys, such as brass, bronze, monel 
metal or aluminium bronze. The value of copper for chemical plant lies in its good 
heat conductivity and resistance to corrosion by a wide range of chemical compounds. 

Copper is extensively used in plant for the food industries, brewing, distilling, 
and sugar refining, and tinned copper vessels are used in milk processing. A large 
tonnage of copper is used in plant required to resist attack by common salt and brine. 
A good summary of such uses is given in a brochure on " Copper in Chemical 
Plant," published by the Copper Development Association (1956). 

Copper sulphate for electroplating is covered by British Standard Specification 
B.S. 2867:1957. The salt is required to be in the form of blue crystals corresponding 
approximately to the formula CuS0 4 . 5H 2 0, and to be free from extraneous matter, 
particularly chromates, nitrates and organic compounds. The material must 
contain not less than 24 per cent, of copper and the following impurities, if present, 
shall not exceed these percentage limits: Ni, 0-3; Fe, 075; insoluble matter, 1; 
chlorides, calculated as CI, 002. The limit for arsenic is 15 p.p.m. 

Alloys. Copper is a major constituent of a large proportion of the non-ferrous 
alloys used industrially. Such alloys include copper-tin (bronzes) {see p. 616); 
copper-zinc (brasses) {see p. 714); the copper-zinc-nickel group {see p. 406), 
copper-nickel (Monel metal) (see p. 405); nickel-silver (see p. 406); and the 
aluminium bronzes. 

Silicon copper of three grades is dealt with in A.S.T.M. Specification No. 
B 53-46, which permits the alloys to be supplied in the form of shot, lumps, ingots, 
or notched slabs of a size that can be handled conveniently and to have the chemical 
composition shown in Table 57. 

Table 57 

Silicon-Copper. A.S.T.M. B 53-46 

Alloy A 

Alloy B 

Alloy C 

Per cent. 

Per cent. 

Per cent. 

Silicon, Si ...... 


18-5-21 -5 


Tin, Sn, max 




Zinc, Zn, max. .... 




Iron, Fe, max. . . 




Aluminium, Al, max. 




Calcium, Ca, max. 




Copper, Cu . . . . 




The sum of copper + silicon + iron, Cu + 

Si + Fe, min. 




Phosphor copper according to A.S.T.M. Specification No. B 52-48 should 
conform as regards chemical composition to that shown for either Alloy A or 
Alloy B in Table 58. 



Table 58 

Phosphor Copper. A.S.T.M. B 52-48 

Alloy A 

Alloy B 

Phosphorus, P, min. 

Phosphorus + Copper, P + Cu, min. 

Iron, Fe, max 

Per cent. 

Per cent. 

Silicon-bronzes are useful in chemical engineering as the addition of silicon up to 
about 5 per cent, increases the strength of the alloy and its resistance to corrosion, 
particularly by acids. Details of the composition of the above alloys and uses will be 
found in the special brochures issued by the Copper Development Association, of 
London, England. 

A copper alloy known as aluminium bronze in the form of plate, sheet, strip and 
rolled bar of the grade commonly used for drawing, forming, stamping and bending 
is dealt with in A.S.T.M. Specification No. B 169-55, which requires the alloy to have 
one of the three chemical compositions shown in Table 59. 

Table 59 

Aluminium Bronze, Plate, Sheet, etc. A.S.T.M. B 169-55 

Alloy A 

Alloy C 

Alloy D 

Copper, Cu 

Aluminium, Al ..... 

Iron, Fe 

Copper + Aluminium + Iron, Cu + Al + 
Fe, min. 

Per cent. 
0-50, max. 


Per cent. 
0-50, max. 


Per cent. 



Copper Powder. In addition to the several forms of coherent copper, there is an 
increasing demand for copper powder for use in powder metallurgy and as a com- 
ponent of anti-fouling paints. The various types of powder marketed may be roughly 
divided, according to their physical characters into (1) dendritic; (2) bronze or 
flake; (3) other types. 

Dendritic copper powder is a mixture of skeleton crystals produced by the 
electrolysis of a soluble copper salt, such as the sulphate, using a high current 
density of over 200 amperes per sq. ft. of surface so as to produce on the cathode 
a loose deposit or a brittle sheet which can be easily ground to powder. As such 
powders are usually finer than the customary testing sieves, fineness is specified in 
terms of apparent density, often less than 1 -2. 

Copper powder is much used for making, by powder metallurgy, porous bronze 
or copper-lead bearing filter discs and friction plates, and similarly, in conjunction 
with graphite for making electric motor brushes. It is also used as a pigment {see 
p. 161). 




The most important salt of copper is the sulphate, CuS0 4 .5H 2 0, which serves 
as the basis for the preparation of most other copper compounds used industrially, 
either for copper plating, as fungicides in agriculture, or other purposes. It is 
usually prepared by the action of hot sulphuric acid on copper in the presence of air. 

The production of copper sulphate in Great Britain for the years 1956-9 was 
50,064, 43,905, 28,049 and 31,508 long tons respectively. 

Industrial Uses. Substantial quantities of copper sulphate are used by mining 
companies in flotation processes, particularly for treating lead-zinc and gold ores. 
It is also used in some textile dyeing processes, in the manufacture of certain types 
of rayon fibre, in leather dressing, as a preservative for timber and in anti-fouling 

Agricultural Uses. Copper compounds are widely used as fungicides and in- 
secticides for the protection of crops. It has been estimated that the world's annual 
consumption of copper salts for these purposes requires nearly 90,000 tons of copper, 
mostly in the form of copper sulphate, the largest demands coming from the United 
States, Central America, France and Italy. 

The salt most commonly used as a fungicide is copper sulphate, often called 
" blue vitriol," which is the chief component in such preparations as Bordeaux and 
Burgundy mixtures. Copper sulphate is sometimes used alone as a winter spray for 
trees, for the destruction of weeds or alga? in ponds, and for killing snails. Other 
copper compounds used as fungicides, but to a much smaller extent, include the 
carbonate, acetate, some cupro-ammonium compounds and cuprous oxide. 

Most copper fungicides have but little effect alone on insect life, but copper 
aceto-arsenite (known as Paris green, emerald green or schweinfurter green) is 
probably the most useful for this purpose. It is prepared by boiling together suspen- 
sions of white arsenic and basic copper acetate with a little acetic acid. Although 
Paris green is not now so widely used as an insecticide as formerly, it is very useful 
for the destruction of mosquito larvae in stagnant pools. It is also used as a poison 
bait for slugs and leatherjackets. 

In the United States the consumption of copper sulphate for agricultural 
purposes totalled 20,800 short tons in 1958. In 1957 the United States exported 
33,800 short tons of copper sulphate to Central America for use as a fungicidal 
spray for agriculture, particularly on banana plantations. The demand, however, 
fell in 1958 to 7,600 short tons owing, it is stated, to the substitution of oil for 
spraying banana plantations. 

Cuprous oxides having colloidal properties may be produced by electrolysis and 
are claimed to be better fungicides than the product obtained by chemical processes. 
Red cuprous oxide is also used as a fungicide. 

A booklet, Copper Compounds in Agriculture, published by the Copper Develop- 
ment Association in 1948, gives much useful data, as also does Uses of Copper 
Sulphate, published by the British Sulphate of Copper Association Ltd., which 
includes a comprehensive list of plant diseases which respond to copper fungicides. 

Copper Plating. British Standard Specification No. 2884 : 1957 for copper 
cyanide for electroplating requires that it shall be in the form of a cream coloured 



powder and shall correspond approximately to the formula CuCN. The material 
shall contain not less than 69 per cent, copper, calculated as metal, and not less 
than 27-5 per cent, cyanide, calculated as (CM). Impurities if present shall not exceed 
the following percentage limits: iron, calculated as Fe, 05; chloride, calculated as 
Q 0-4; insoluble matter 015. 

Copper Pigments. Copper is used in the paint industry principally in the form of 
copper powder, bronze powders and cuprous oxide. The natural carbonates of 
copper, malachite and azurite, after careful selection and grinding are sometimes 
used for making brilliant blue paints, but not commonly, owing to their cost. 

In the paint industry dendritic powders are employed chiefly in anti-fouling 
paints for pleasure craft. 

Flake copper powder is used in anti-fouling paints (often in conjunction with 
salts of mercury or arsenic) in decorative finishes for indoor use, printing inks and 

Flake copper powders, as the name implies, consist of the metal in the form of 
minute flakes. It is commonly made by stamping thin sheets of copper in a stamp 
mill, together with a fatty lubricant, such as stearic acid. Flake copper, which has a 
greater hiding power than the dendritic powder, is often produced from copper 
alloyed with about 2 per cent, of zinc, but oxygen-free, pure copper may be used. A 
process has been recently introduced for producing the flakes by electrolytic de- 

A tentative specification, D 964-48T formulated by the A.S.T.M. requires that 
copper powder for use in anti-fouling paints shall contain a minimum of 99 per cent. 
of copper and be of such fineness that not more than 1 per cent, is retained on a 
No. 325 (44 micron) sieve. 

Copper bronze pigments are produced from copper-zinc-aluminium alloys by 
first reducing the alloy to small size, either by granulation or by rolling into thin 
sheets and clipping, and then flaking in stamp or ball mills in the presence of a 
lubricant. The flakes so produced, after being graded, are polished in rotating drums 
in order to produce the " leafing " quality necessary for use in printing inks and 

The colour of copper bronze powders varies with the composition of the alloy 
used. A pale gold bronze is obtainable from an alloy composed of copper, 92 per 
cent. ; zinc, 6 per cent. ; aluminium, 2 per cent. ; whereas green gold bronze is yielded 
by one composed of copper, 68-75 per cent.; zinc, 31 per cent.; and aluminium, 
0-25 per cent. A fairly wide range of other colours can be obtained by heat-treating 
the powders. 

Red cuprous oxide has found increasing use in recent years as a pigment in anti- 
fouling paints for the protection of steel and wood against corrosion and marine 
growths in sea-water. It is also used as a fungicide in agriculture, for colouring glass 
and in some ceramic products. It was formerly produced chiefly by the anodic 
oxidation of copper in an alkaline salt solution, but, more recently, a pyro-metal- 
lurgical process has been introduced in which pure ribbon copper is oxidized at 
about 920° C. in the presence of steam. The oxide mixture which results is next 
converted to cuprous oxide by a secret process. 

M.C.A.I.— a 161 


The A.S.T.M. tentative specification D 912-47T for cuprous oxide for use in 
anti-fouling paints requires the product to conform to the requirements shown in 
Table 60. 

Table 60 

Cuprous Oxide for Use in Anti-fouling Paints. A.S.T.M. D 912-47T 

Cuprous oxide, min. . 

Total copper, calculated as Cu, min 

Total reducing power calculated as Cu 2 0, min. . 

Metals other than copper, max. 

Combined chlorides, calculated as CI, and sulphates calculated as 

SO,, max. 

Acetone-soluble matter, max. 

Stability: decrease in total reducing power after stability test, max. 

Coarse particles retained on No. 325 (44 micron) sieve, max. 

Total nitric acid-insoluble residue on a No. 200 (74 micron) sieve, 


Per cent. 




Copper naphthenate, which is made either from copper sulphate or acetate and 
commercial naphthenic acid, is finding increasing use as a fungicide to protect 
timber and textile fabrics and as a mildew-proofing agent in the paint industry. 

During World War II, copper naphthenate was used for the protection of canvas 
tents, ropes and sandbags, and it is included in U.S. Army Specification No. 100-17 : 
B.S.S./A.R.P. 56, 57 and 58. Mixtures of metallic naphthenates and chlorinated 
phenols are also included in U.S. Navy Specifications 52W5, 1945. 

Waterproofing Compounds. Copper formate and copper stearate are used for 
waterproofing and rotproofing textiles. Copper formate is made by Imperial 
Chemical Industries Ltd. at their Maryhill factory, Glasgow, by the direct reaction 
of copper sulphate and calcium formate at 70-80° C. It is stated to be suitable for use 
in a one-bath process for " lightproofing." Copper stearate is made by the reaction 
of basic copper carbonate with a mixture of fatty acids at 70° C. It is stated to be 
preferable to the formate for heavyproofing. 


" Copper Oxide Rectifiers." Science Library Bibliogr. Ser. No. 357, 1937. (176 references.) 

" Red Cuprous Oxide " [Prepn. and Use in Paints]. By J. E. Drapeau. " Protective and Decor- 
ative Coatings." Ed. by J. J. Mattiello. Lond., 1942, Vol. 2, pp. 329-33, including 
bibliography. . 

" Metallic Copper Powders " [Prepn. and Use in Paint]. By S. B. Tuwiner. " Protective and 
Decorative Coatings." Ed. by J. J. Mattiello. Lond., 1942, Vol. 2, pp. 576-84. 

" Bronze Powders " [Prepn. and Use in Paint]. By D. O. Noel. " Protective and Decorative Coat- 
ings." Ed. by J. J. Mattiello. Lond., 1942, Vol. 2, pp. 585-601. 

" Modern Copper Smelting: A Review of Changes and Improvements." By R. A. Wagstaff. 
Metal Ind., 1944, 64, 327-9. 

" Copper Smelting: A Short Review of Some Present-day Developments." By W. H. Dennis. 
Mining Mag. (Lond.), 1944, 71, 9-15. 

" Copper and Its Alloys." By J. W. Donaldson. Metal Ind., 1944, 64, 274-6, 290-6, 315-9. 

" Coloured Glasses: A Monograph prepared for the Society of Glass Technology." By W. A. 
Weyl. /. Soc. Glass Tech., 1944, 28, 158-266 (Copper, pp. 189-202). 



" Metallurgy of Copper." By F. R. Pyne. " Handbook of Non-ferrous Metallurgy." Ed. by 

D. M. Liddell, 2nd Ed., Lond., 1945, pp. 227-74: 
" Hydrometallurgy of Copper." By H. A. Tobehnann, ibid., pp. 345-69, including bibliography. 
" Action of Anti-fouling Paints." By J. D. Ferry and B. H. Ketchum. Industr. Engng. Chem, 

{Industr. Ed.), 1946, 38, 806-10. 
" Copper Arsenite." By P. Miller. Industr. Engng. Chem., 1947, 39, 1521-30. 
" Copper Compounds in Agriculture." Pub. No. 41. Copper Development Assn., 1948, 117 pp. 
" Chemistry and Use of Insecticides." By E. R. de Ong. New York, 1948, 345 pp. (Copper and its 

Compounds, pp. 41-65, including bibliography.) 
" Recent Progress in the Metallurgy of Copper and Copper Alloys." By M. Cook. 4th Empirt 

Min. Met. Congr., Lond., 1949, 20 pp., including bibliography. 
" Some Modern Developments in Copper Pyrometallurgy (with special reference to American 

Practice)." By W. B. Boggs. 4th Empire Min. Met. Congr., Lond., 1949, 15 pp. 
" The Fire-refining of Copper." By H. J. Miller. " The Refining of Non-ferrous Metals." Inst. 

Min. Met., Lond., 1950, pp. 145-84, including bibliography. 
" Manufacture and Application of Copper Naphthenate." By A. Davidsohn. Industr. Chem., 

" The Cupriferous Pyrites Industry." By L. C. Hill. Bull Inst. Min. Met., 1950 (June), No. 523, 

pp. 1-12. 
" Copper and Its Alloys in Engineering Technology." Copper Development Assn., Lond., 1949, 

87 pp. 
" The Electrolytic Copper Refinery of the Rhodesia Copper Refineries Ltd. at Nkana, Northern 

Rhodesia." By W. J. Friggens, E. W. Page and T. Milligan. " The Refining of Non- 
ferrous Metals." Inst. Min. Met., Lond., 1950, pp. 203-27. 
" Uses of Copper Sulphate." British Sulphate of Copper Association, Lond., 1952, 30 pp. 
" Copper, The Science and Technology of the Metal, its Alloys, and Compounds." By Allison 

Butts. N.Y. and Lond., 1954, 936 pp. 
" Classification of Copper and Copper Alloys." Copper Development Assn., 1956, 27 pp. 
" Copper in Chemical Plant." Pub. No. 23. Copper Development Assn., 1956, 68 pp. 
" Copper." By Jean Isabey. Nouveau Trait6 de Chimie Mineiale, Ed. by P. Pascal. Paris, 1957, 

Vol. Ill, pp. 155-421. 
" Copper." By A. D. McMahon. " Mineral Facts and Problems." U.S. Bur. Mines Bull. 585, 

1960, 25 pp. 
" Copper," U.S. Bur. Mines, Minerals Yearbook (Annual). 


American Society for Testing Materials 
A.S.T.M. Standards, 1958: 

Electrolytic cathode copper. B 115-43. 

Electrolytic copper, wire, bars, cakes, etc. B 5-43. 

Oxygen-free electrolytic copper, wire, bars, billets, etc. B 170-47. 

Fire refined copper for wrought products and alloys. B 216-49. 

Fire refined casting copper. B 72-55T. 

Lake copper, wire, bars, cakes, slabs, ingots. B 4-42. 

Silicon Copper. B 53-46. 

Phosphor Copper. B 52-48. 

Aluminium bronze, plate, sheet, etc. B 169-55. 

Cuprous oxide for use in anti-fouling paints. D 912-47T. 

Copper powder for use in anti-fouling paints. D 964-48T. 
British Standards Institution : 

Cathode copper, B.S. 1035 : 1952. 

Electrolytic tough pitch high conductivity copper. B.S. 1036 : 1952. 

Fire refined tough pitch conductivity copper. B.S. 1037 : 1952. 

99-85 per cent, tough pitch copper i conductivity i B.S. 1038 : 1952. 

99-75 „ „ „ „ „ [ not \ B.S. 1039 : 1952. 

99-50 „ „ „ „ „ ' specified * B.S. 1040 : 1952. 

Phosphorus deoxidized non-arsenical copper for general purposes. B.S. 1 172 : 1952. 

Tough pitch arsenical copper. B.S. 1173 : 1952. 

Phosphorus deoxidized arsenical copper. B.S. 1174 : 1952. 

Oxygen-free High Conductivity Copper. B.S. 1861 : 1952. 

Copper Cyanide for Electroplating, B.S. 2884 : 1957. 

Copper Sulphate for Electroplating. B.S. 2867 : 1957. 
U.S. National Stockpile Specification : 

Copper- P16-R3, 10th August, 1956. 

o2 163 


The corundum group includes the gemstones ruby and sapphire, common corundum 
and emery, but in view of the diversity of uses for these minerals they will be dealt 
with separately. In recent years corundum and emery have become of relatively 
minor importance owing to the increased use of artificially prepared electric furnace 


Corundum, a naturally occurring anhydrous oxide of aluminium, varies con- 
siderably in colour from blue, green, grey, brown to black, and has a specific 
gravity varying from about 3-7 to 4. It breaks with a conchoidal fracture and, 
although the fresh mineral shows no cleavage, the altered mineral often splits 
along planes of separation or partings, thus reducing its value as an abrasive. 
Although corundum has a hardness of about 9, which is next to that of diamond, the 
hardness of different types may vary considerably. 

Corundum is usually found associated with felspathic rocks in South Africa and 
India and with nepheline syenites in Canada. 

Common corundum, such as is used for the manufacture of abrasive wheels, 
occurs native in the following forms: (1) crystal corundum, often found in all sizes 
in eluvium resulting from the disintegration of corundum-bearing rocks; (2) 
boulder corundum; (3) lode or reef corundum. 

World Production 

The world's total production of marketable corundum varied between about 
1,520 long tons in 1938 to about 9,800 long tons in 1958 (including an estimated 
3,400 long tons from the U.S.S.R.). 

Deposits of corundum in the Union of South Africa occur over a wide area in 

Table 61 

World Production of Corundum* 

Long tons 











S. Rhodesia 






Union of S. Africa 


















Australia . 











* From Mineral Resources Division, Overseas Geological Surveys, London. 
t Exports. 



the Zoutpansberg district of the Northern Transvaal, worked by the American 
Abrasive Company (Pty.) Ltd., and in the Pietersburg district in Eastern Transvaal 
worked mainly by diggers. At one time about three-quarters of the world's produc- 
tion of natural corundum came from the above deposits, but in recent years their 
importance has declined and Southern Rhodesia now records the largest production 
as shown in Table 61 . 

Preparation and Marketing 

The milling of corundum is normally done by crushing, screening and water 
classifying, the object being to remove waste rock while retaining the desired shape 
and size of the grains or particles. The crushed grains are often tested for specific 
gravity before they are packed for shipment, so as to ensure a standard of purity. 

According to Kupferberger, certain physical characteristics shown by hand 
specimens of crude corundum, and summarized below, afford a useful guide for its 
possible value as an abrasive. 



Lustre .... 


Cleavage or parting 

Bright, glassy to adam- 

Uneven or splintery. 


Absent, or as few as 

Dull to pearly. 

Smooth or even. 
Well developed. 
Presence of mica, rutile, 
ilmenite, etc. 

As a general rule, however, the industrial value of corundum as an abrasive 
can only be decided by practical trials. 

Natural corundum finds its largest market in the United States, where it has to 
meet keen competition from artificial abrasives such as carborundum (silicon car- 
bide) and fused alumina products. As the natural mineral from different sources 
varies somewhat in its abrasive properties, it is essential that it should be carefully 
graded before export. 

In the Union of South Africa, the Government does not permit the mineral to be 
exported until it has been certified by the Chief Grader, or his Deputy, whose func- 
tions are laid down by the Restricted Minerals Export Act, No. 35 of 1927, and Regu- 
lations issued thereunder. According to the Corundum Export and Grading 
Regulations, corundum for export is classified as (a) boulder corundum; (6) crystal 
corundum; (c) corundum concentrates.; (d) grain corundum. Boulder corundum 
is defined as any corundum-bearing rock which has not undergone any mechanical 
treatment except breaking to convenient size. Crystal corundum consists of crude 
corundum crystals derived from eluvial deposits or from weathered reef deposits in 
situ. Corundum concentrate is the product obtained by crushing and concentrating 
any corundum-bearing rock to eliminate the waste and gangue materials, but it is 
ungraded according to size. The name grain corundum is applied to concentrate 
further prepared and graded to size. 



Before a consignment of " crystal " corundum can be exported it must be 
subjected to chemical analysis to determine its alumina content, and also to a 
screening test. The grading on the basis of alumina content is as follows: 
A— containing not less than 92 per cent. AI2O3. 

B — „ less „ 92 „ „ but not less than 90 per cent. AI2O3. 

c — » „ „ 90 „ „ but not less than 85 per cent. AI2O3. 

D— „ „ „ 85 „ „ AI2O3. 

Grading for size is as follows: 

1 — Coarse — retained on a round hole screen of \ in. diam. 
2 — Medium — undersize on \ in. round hole screen and oversize on J in. 
3 — Fine undersize on | in. round hole screen and oversize on \ in. 
4 — Mixed — All oversize on £ in. round hole screen. 

The various grades of crystal corundum are designated for export so as to 
indicate alumina content and size. Thus A2 indicates a product having not less than 
92 per cent, of alumina and of medium size, as defined above. 

Corundum " concentrate " is classified according to alumina content only. 
In order to get a payable percentage recovery and a concentrate with over 92 per 
cent, alumina it is necessary to crush the rock so that all of it could pass through a 
screen of 8-mesh to the linear inch. The size of the grains in the concentrate therefore 
ranges from J in. downwards. 

" Grain " corundum is classified on the basis of its alumina content and is also 
graded in various commercial sizes required by the user and approved by the Chief 
Grader. Some users, in addition to specifying the alumina percentage, also require 
the mineral to have a specific gravity of not less than 3 -70 and to contain not more 
than 10 per cent, of silica (Si02> and 5 per cent, of iron oxide (Fe203). 

South African corundum has the advantage that, on crushing, it breaks down 
gradually and continuously into sharp-edged, facetted particles, so that, when used 
for grinding, it always presents a surface which is fresh and cool. This property is an 
advantage when grinding and polishing optical instruments and lenses, and for 
making abrasive wheels. 

The thirteen sizes of grain corundum used in the United States for grinding and 
polishing optical lenses range from 60 to 275-mesh. For use in abrasive wheels, 
eleven sizes are used, varying from 8 to 54-mesh. The grades most in demand in the 
United States are designated in the South African classification as A-l, A-2, B-3 
and C-4. In addition, five finer grades, termed " flour " and used for fine polishing, 
are separated from the crushed mineral which passes a 220-mesh sieve, these grades 
being determined by the time the flour takes to settle in water. 

The U.S. National Stockpile Material Purchase Specification P-18 of January 
3rd, 1951, covers three grades each of natural crystal corundum, and corundum 
concentrates primarily intended for abrasive purposes. These products are required 
to comply with the specification in regard to (1) corundum content; (2) size; (3) 
abrasive value and grain breakdown: methods are detailed for carrying out these 



The rundum content, as determined by a leach-petrographic test, must not be 
less thi the following percentages: 

Grade Crystal Corundum Crystal Concentrate 

Per cent. min. Per cent. min. 

A . . . 87-5 85-5 

B . . 85-5 83-5 

C . . 800 800 

Tb ach-petrographic test is carried out as follows: place 1 gm. of the 80 grain 
materi prepared by crushing and sieving a representative sample by a specified 
methoi n a large platinum crucible and add 15 c.c. of strong sulphuric acid and 
20 c.c. lydrofiuoric acid. Place on the water bath or sand bath and evaporate until 
all the 7 is expelled; finally heat until fumes of SO3 come off copiously. Transfer 
to a be ;r and add 20 c.c. of hydrochloric acid, place on the hot plate and heat for 
twenty inutes to dissolve all the soluble sulphates. Dilute to 70-100 c.c. with hot 
water I heat for ten minutes longer. Filter and wash first with hot 5 per cent. 
HC1, t 1 hot water, then three times with warm 10 per cent. KOH, then again with 
water, lite and weigh as corundum. Examine the residue with the petrographic 
micros pe for the presence of other insoluble minerals such as kyanite and rutile. 
If thes re present, a petrographic grain count is made of the residue to obtain the 
correc value. 

Tb 2& requirements specify that, for grade A crystal corundum, not more than 
5 per 1 t. shall pass a 3-mesh U.S. Standard screen. For crystal grades B and C the 
limit 5 per cent, passing a 7-mesh U.S. Standard screen. Crystal corundum 
conce ates are required to be approximately J in. to 16-mesh in size, with not more 
than .' :r cent, passing a 20-mesh U.S. Standard screen. 

Tl abrasive value and grain breakdown is determined by means of the U.S. 
Natic I Bureau of Standards Field Abrasion Tester (N.B.S., T.R. 1482). Briefly, 
the te xmsists in comparing the abrasive properties of the corundum with that of a 
stanc 1 abrasive, E.L. Alundum X, when used on an abrasive wheel working 
agaii a specimen of a standard plate glass. Certain minimum values are specified 

for t ratio between the abrasive effect of the natural corundum and the standard 

artificial abrasive. 

The grain breakdown test is carried out at the same time as the abrasive test and 
is based on the fact that grains of an abrasive break down into smaller particles in 
use and so their grinding efficiency is reduced. By repeating the test ten times with 
the same portion of the sample, the ratio of the breakdown rate as compared with 
that of the standard abrasive can be ascertained and minima for such ratios for each 
of the six types of natural corundum are specified. 


The chief abrasive use for corundum is in finishing heavy iron and steel castings, 
grinding and polishing optical lenses, glassware, building stones and gemstones. It 
is also used for lining grinding mills and as grinding balls. Certain varieties, such as 
that from S. Rhodesia, are mainly used in making refractories and it is stated that 



corundum from Namaqualand is more suitable for making refractories than for use 
as an abrasive. 

Large quantities of artificial corundum (fused alumina) are produced for abrasive 
purposes; the properties of this material are dealt with in this volume in the section 
on Aluminium {see p. 24). 

Statistics of the production of artificial corundum are not generally available, but 
it is interesting to note the following exports (in long tons) in 1958: France, 5,613; 
Germany, 14,368; Sweden, 706; Italy, 318. Natural corundum for abrasive purposes 
is characterized by its prominent basal cleavage which causes crystals to break 
readily with smooth, flat faces at right angles to the axis of elongation, through 
successive reductions in size. 

Corundum for abrasive purposes, in addition to being employed in the form of 
loose grains, is also used as a coating for abrasive paper or cloth and in the prepara- 
tion of bonded grinding wheels, or sharpening stones. Grinding wheels may be 
produced by calcining a mixture of corundum, clay and felspar, or by the use of 
sodium silicate as a bonding material. The so-called elastic abrasive wheels have 
rubber or shellac as the bonding material and more recently synthetic resins, such as 
bakelite, have been similarly used. 

Finely ground corundum, bonded with clay, has also been used for making 
refractory crucibles. For this purpose, the mineral should be ground to pass a 
200-mesh screen; its content of alumina should be about 90 per cent., and its iron 
oxide content should not greatly exceed 3 per cent. No limit is put on the percentage 
of silica, but felspar is objectionable. 

Some rather low grade corundum has been used in the preparation of non-slip 
treads on ceramic tiles and concrete slabs. Corundum for this purpose may have a 
fineness of about 120-mesh and its content of iron should be preferably under 2 per 
cent. ; felspar is not objectionable. For cement tiles a coarse grade of corundum is 
used, often between 20- and 40-mesh. 


The name sapphire is applied to natural or synthetic stones consisting of alum- 
inium oxide, AI2O3, in a transparent crystalline form. It has the same composition 
and structure as the mineral corundum. Sapphire may be colourless (white sapphire), 
or coloured (blue or other tints) depending upon the presence of impurities, such as 
titanium in the crystal lattice. 

Natural sapphire is known to occur in Ceylon, Kashmir, Cambodia, Thailand, 
Australia, the Union of South Africa and the United States, and is usually employed 
as a gemstone. At one time natural sapphire was used for industrial purposes, but 
it has been displaced almost entirely by the synthetic mineral, of which regular 
supplies of guaranteed quality can be assured. 

Synthetic sapphire has been produced in Europe by a process invented by A. 
Verneuil in 1902, but no production took place in Great Britain until 1940 and in the 
United States until 1941 ; the industry until then centred in France, Switzerland and 



The method of producing synthetic sapphire is basically the same as that invented 
by Verneuil. A stream of finely powdered very pure alumina is continuously 
projected on to an oxy-hydrogen flame which impinges on the tip of a ceramic 
holder, upon which a crystal boule is slowly built up. The boules produced weigh 
about 80-125 carats and take about 2} hours to form. These boules can be split 
longitudinally into two halves if tapped with a hammer and the half boule can be 
worked up into the desired shape for industry. The process has also been adapted to 
give a cylindrical crystal rod which needs much less dressing to yield industrial 
shapes than do the boules, and so a saving is effected in diamond dust. 

The starting point for the preparation of the alumina powder is highly purified 
ammonium alum, NH4A1(S04)2.12H 2 0, crystals which are heated in a silica tray 
for two hours at 1,000°C. The alum decomposes and swells up to a sponge-like 
mass of y alumina, which is later broken down to a very fine powder. If red sapphire 
is required chromic sulphate is added to the ammonium alum so as to give 0-5 to 
5 per cent. Q-203 in the calcined powder, the amount depending on whether a 
pale pink or deep ruby colour is required. Blue sapphires are produced by adding 
oxides of iron and titanium. 

Synthetic sapphire has been made in Great Britain for many years past by 
Salford Electrical Instruments Ltd., of Heywood, Lancashire, a subsidiary of the 
General Electric Company. Several grades of material are available: (a) half boules, 
cleanly split and free from flaws or imperfections; (b) half boules, which have not 
split cleanly, or show slight flaws or are slightly below normal size; (c) irregularly 
shaped small pieces or cracked whole boules. An average boule, when split in 
half, measures about 2 in. in length, | in. in width, i in. in depth and weighs about 
25 gm. (125 carats). The material is supplied either clear or in a range of ruby 

In the United States synthetic sapphires for both industrial and gem uses are 
produced by the Linde Company, a division of the Union Carbide Corporation 
of New York. The gem varieties are marketed as " star " sapphires or " star " 
rubies at prices about one-eighth of those of the natural stones. The sizes of 
industrial sapphire marketed by the Linde Company include rods up to 3 ft. in 
length and of 005, 010, 015 and 0-20 in. diameter, and boules of 2 to 5 in. long 
weighing 75 to 500 carats, though considerably larger ones have been made. 

It was reported in 1957 that the Bell Telephone Company of the U.S.A. were 
producing hydrothermally synthetic sapphire as large as i in. x | in. x £ in. by a 
method analogous to that used for making synthetic quartz. A silver lined autoclave 
is about three-quarters filled with one molar sodium carbonate. Alumina or 
aluminium hydroxide is introduced into the bottom of the reaction cavity and seed 
crystals of corundum are suspended at the top. At an operating temperature of over 
400°C. and a pressure of 30,000 lb. per sq. in., the nutrient first dissolves in the 
sodium carbonate until the latter is super-saturated and then deposits on the seeds. 
The rate of growth is about 01 in. per day. 

In 1944 the British Ministry of Aircraft Production (now the Ministry of Supply) 
issued a specification for synthetic sapphire boule. This required that the boule 
should split readily and cleanly down its longitudinal axis into two approximately 



equal halves and the faces so exposed should be substantially plane for about 75 per 
cent, of their length. The material had to be free from spurious colour tinges, but a 
slight blue tinge was allowable if it was evenly distributed. The appearance of the 
half boules had to correspond to the following requirements: (a) the face of the 
fracture to be free from deep veins, cross-hatching, wavy surface and deep curves; 
(b) any striation present to be slight and confined to the edges of the boule; (c) 
the internal structure to be free from fractures, inclusions and bubbles. When 
immersed in methylene iodide or other liquid of similar refractive index in a glass 
flask standing on a black background, e.g. velvet, the half boules should appear 

The U.S. National Stockpile Specification P-50 of November 1, 1947, covers 
synthetic sapphire and synthetic ruby suitable for the manufacture of jewel bearings. 
The term sapphire as used here means synthetic corundum of jewel-bearing quality, 
colourless or white in colour. The term ruby means synthetic corundum of jewel 
bearing quality and clear ruby in colour. All material purchased under this Specific- 
ation shall be synthetic and shall be equal, or superior, to material of " Linde 
Air Products Corporation Grade A Jewel-Bearing Quality " 1944 classification. 
Material shall be in the form of half boules, pieces or rods. The Specification 
further requires that: (a) half boules and pieces shall have a minimum individual 
weight of 35 carats, be clear in colour, and no piece shall contain more than two 
lateral cracks. No piece shall contain lateral cracks, crown cracks, bubbles, layers or 
other imperfections to a total extent rendering more than 10 per cent, of its total 
volume unsatisfactory for the manufacture of jewel bearings; (b) rods shall be 
either 080 in. or 0-125 in. nominal diameter as specified by the purchaser, and 
shall be not more than 0005 in. under, or 0010 in. over, the specified nominal 
diameter. Pieces shall be not less than one inch in length. Rod shall be clear in 
colour and shall be free from all cracks and feathers. No rod shall contain more 
than three layers or bubbles per inch. No rod shall contain imperfections to a total 
extent rendering more than 10 per cent, of its volume unsatisfactory for the 
manufacture of jewel bearings. 

Synthetic sapphire, which crystallizes in the hexagonal system, has a hardness of 
9 on Mohs's scale (i.e. equal to that of tungsten carbide), conchoidal fracture, 
specific gravity 3-99, specific heat 018 (at 25°C), melting point 2,050°C, electrical 
resistance 10 11 ohm/cm. (at 500°C.) and 10 3 ohm/cm. (at 2,000°C). Its optical 
properties are of interest particularly on account of its high transmission of ultra- 
violet or infra-red radiation. For this reason sapphire domes and windows are 
used in looming mechanism for guided missiles. 

Synthetic sapphire is also used as prisms and lenses in the construction of photo- 
cells sensitive to infra-red radiation, as a 1 mm. thick window transmits about 70 
per cent, of a 5-5 y. radiation. Round transparent sapphire windows are available as 
discs of f to 11 in. diameter and thicknesses ranging between 1 and 3 mm., or in 

On account of its hardness, synthetic sapphire is used for long-wearing pivot 
bearings for scientific instruments, knife-edged bearings for balances, extrusion dies, 
and gramophone styles for fine groove long playing records. 




Thi mportant natural abrasive consists of a mechanical mixture of granular 

rune 1 with various impurities, such as magnetite, the amount of corundum 

ely ceding 50 per cent, and often being much lower. Its specific gravity varies 

>m ,• iut 2-7 to 4-3, depending on the amount of impurities present, and its 

rdn between 7 and 9. As a rule the impurities are so finely divided and intimately 

soci d with the corundum that their separation is not commercially possible. 

Tf percentage of alumina in commercial emery may vary from 40 to 75 per 

;nt., it the value of the mineral depends, not upon its chemical analysis, but 

lain m its physical properties. As with commercial grain corundum, the hardness 

nd i asive properties of emery from different localities vary considerably. 

I :ry may be roughly divided into three main types: (1) true emery, which 
cor i of a mixture of corundum and magnetite, the best examples being the 
' azlxl and Turkish products; (2) spinel emery, which is a mixture of spinel, 
jrundum and magnetite, and has been worked chiefly in New York State and 
Virginia, U.S.A. ; in recent years production has come only from Peekshill, N.Y. ; 
(3) felspathic emery, which is similar to (2) but contains from 30 to 50 per cent, 
plagioclase felspar. Grecian, or Naxos, emery is characterized by its high content of 
alumina, stability under heat and hard sharp grains. Turkish emery is rather softer 
and, as it is not stable under heat and breaks down under pressure, is seldom used 
for making grinding wheels. It is best suited for the manufacture of emery cloth or 
paper, in setting up polishing wheels and in pastes and compounds. American 
emery, being softer that either Greek or Turkish material, is now used mainly in 
pastes and compositions. 

Methods of dressing crude emery for the market vary somewhat. In the United 
States, the mineral is broken in jaw crushers (mica being removed by upward air 
currents) and is then passed through long troughs and over shaking screens, which 
produce 30 sizes, i.e. 12 grades between 6- and 46-mesh (termed " coarse-grained "), 
12 sizes between 54- and 220-mesh (termed " fine-grained "), and 4 grades of " flour." 

World Production 

Complete statistics of production in recent years are not available, but in 1958, 
3,363 long tons came from Turkey, 6,863 long tons from the United States, and 
Greece exported 5,872 long tons. Emery is also produced in the U.S.S.R., Germany 
and Austria. 


The use of emery as an abrasive dates from ancient times, but its large-scale 
industrial use practically commenced with the invention in 1870 of the emery 
grinding wheel, which is still extensively used for coarse grinding, particularly of 
cast iron. 

Emery is also much used, coated on paper or cloth, in both grain and powder 
form, for finishing cutlery, tools and glass, both optical and plate. Lump emery is 
sometimes employed in mills for grinding talc, whiting, barytes, etc., for use in the 
paint trade. 



The largest use in the United States is as a non-skid component in stair treads, 
floors and pavements. 

So far as can be ascertained, there are no general specifications for emery, the 
value depending upon the purity, hardness and toughness of the product. Users 
generally are unwilling to accept anything but a dressed product, which has been 
ground and graded to size. 

Emery is often preferred for abrasive work where high-grade corundum would 
be too harsh. Greek, or " Naxos," emery is preferred by some users in the United 
States for manufacturing emery grinding wheels. 


" Corundum in South Africa." By A. L. Hall. Union ofS. Africa Geol. Surv. Mem. No. 15, 1921, 

" Abrasives." By V. L. Eardley-Wilmot. Canad. Dept. Mines, Bull. 675, Pt. 2, 1927. (Corundum, 

pp. 1-34; Emery, pp. 36-41, including bibliography.) 
" Abrasives." Anon. Min. Res. Br. Empire & Foreign Countries, Imperial Institute, London, 1929 

(Corundum, pp. 11-20; Emery, pp. 21-8.). 
" Corundum in the Union of South Africa." By W. Kupferberger. Union ofS. Africa Mines, Geol. 

Surv. Bull. No. 6, 1935, 81 pp. 
" Corundum." By R. W. Metcalf. U.S. Bur. Mines, Inform. Circ. No. 7295, 1944, 13 pp. 
" Emery, Occurrences and Characteristics." By S. R. Mitchell. Chem. Eng. Min. Rev. (Melbourne), 

1944 36 121-2. 
" Corundum! A Vital Wartime Abrasive." By R. D. Parks. Mining Tech. (A.M.I.E.), 1945, 9 

(May), Pub. No. 1883, 8 pp. 
" Non-metallic Minerals." By R. B. Ladoo and W. M. Myers. New York, 1951. (Corundum and 

Emery, pp. 166-72), including bibliography. 
" Boule Manufacture, Wiede's Carbidwerk-Bavaria." B.I.O.S. Target. No. C22/2814, 10 pp. 
" Synthetic Sapphire and Spinel Production in Germany." By M. H. Barnes. FIAT Final Rep. 

No. 655, 1945, 17 pp. 
" Jewels and Stones for Industrial Purposes." By H. P. Rooksby. /. Roy. Soc. Arts, 1946, 94, 

No. 4722, 508-522. 
" Gems, Synthetic." By A. K. Seemann. Encyclopedia of Chemical Technology. Ed. by R. E. Kirk 

and D. F. Othmer. New York, 1948, Vol. 7. pp. 157-167 
" Some Industrial Uses of Synthetic Sapphire." By K. W. Brown. Industr. Diam. Rev., 1951, 11, 

No. 129, 169-172. 
" Diamond Technology." By P. Grodzinski. London, 2nd Ed., 1953, 784 pp. (Sapphire, pp. 

35, 423, 430, 440). 
" Commercial Synthesis of Star Sapphires and Star Rubies." By C. Frodel, Min. Engng., 1954, 6, 

No. 1, 78-80. 
" Jewel Bearings." By R. D. Thomas. " Mineral Facts and Problems." U.S. Bur. Mines. Bull., 556, 

1956, pp. 399-407. 
" Synthetic Star Sapphire Spheres." Gemologist, 1958, 23, 189. 
" Sintering Sapphire Spheres." By L. Navias. /. Amer. Ceram. Soc, 1956, 39, 141. 
" Synthetic Sapphire." The Salford Electrical Instruments Ltd., Heywood, Lanes., 6 pp. 
" Synthetic Sapphire, an Infrared Optical Material." By R. D. Olt. Talk delivered at the Infrared 

Information Symposium, 1958, March 5th, 11 pp. including biblio. 
" Optical Properties of Synthetic Sapphire." By R. W. Kebler, The Linde Co., New York, 15 pp. 
" Corundum, Natural versus Synthetic." By E. R. Varley. New Commonwealth, 1959, 37, Jan., 

" Synthetic Sapphire in Electronics." By R. D. Olt. Electronics, 1959, 32, No. 49, 10 pp. 
" Abrasives." By R. B. Ladoo in " Industrial Minerals and Rocks." Amer. Inst. Min. Met. and 

Petrol. Engng., 1960, 3rd Ed., pp. 1-21. 
" Corundum and Emery." By H. P. Chandler. " Mineral Facts and Problems." U.S. Bur. Mines 

Bull. 585, 1960, 6 pp. 
" Properties and Uses of Linde Sapphire." Linde Co., Division of Union Carbide Corporation, 

N.Y., 4 pp. 
" Abrasives, U.S. Bur. Mines, Minerals Yearbook, (Annual). 
" Jewel Bearings." Ibid. 


U.S. National Stockpile Specification: 

Natural Crystal Corundum (for abrasive use). P-18, Jan. 3rd., 1951. 
Synthetic Sapphire and Ruby for Jewel Bearings. P-50, Nov. 7th., 1947. 



Diamond consists of almost pure elemental carbon, and frequently crystallizes in 
the cubic system, octahedron and dodecahedron shapes being the most frequent (or 
modifications of these shapes); twinning is fairly common. Pure diamond is trans- 
parent, colourless, has a specific gravity of about 3-52 and a very low thermal 
expansion. Diamond is a non-conductor of electricity. It has a hardness of 10 
on Mohs' scale or 40-42 on Wooddell scale, being the hardest of all known minerals, 
and has a refractive index of about 2-4175. 

Diamonds most valued as gemstones are usually colourless, or have a very faint 
bluish tinge. Traces of impurity may impart colours, such as pink, blue, yellow or 
green, to the stones and so give rise to the so-called " fancy stones " of the jeweller. 
Diamonds of a yellowish tinge not sufficiently marked for them to be classified as 
" fancy " stones are referred to as " off-colour " and such diamonds can often be 
changed to green by submitting them to alpha-radium radiations. Overlong 
exposure to radiation may result in the stones being turned completely black. 
The green colour is apparently light-permanent, but the original colour may be 
restored by heating the stones at 500° C. or by recurring. In 1957 the United King- 
dom Atomic Energy Authority made its facilities available for the colouration of 
diamond by atomic bombardments. Diamonds irradiated inside a nuclear reactor 
are coloured green but subsequent heat treatment may change the colour to brown. 
Very impure stones are valueless as gemstones, but find use for industrial purposes. 
Most diamond crystals have cleavage planes parallel to the octahedral faces, along 
which the stones can be most readily split, a property which is utilized in the cutting 
of brilliants for gem purposes and for shaping stones for industrial use. 

A variety of diamond, known as carbonado and peculiar to Brazil, is black or 
grey in colour and consists of minute crystalline aggregates, it is slightly porous, has 
a rather lower specific gravity than precious diamond and finds extensive use for 
industrial purposes. 

World Production 

Since about the year 1893 the world market for diamonds has been almost 
entirely controlled by a group of London diamond merchants, generally known as 
the Diamond Syndicate, whose aim it is to stabilize the market by controlling prices 
and the quantity of stones marketed. In 1946 Industrial Distributors (1946) Ltd. 
was formed to handle the sale of industrial diamonds exclusively. Industrial stones 
sold through this company are usually sent from the mines to Johannesburg, while 
the gem stones are sent to Kimberley for sorting and evaluation. All diamonds are 
finally sent to London, where they are sold at what are known as " sights sales," 
which are held several times a year and to which selected dealers and large consumers 
only are invited. About 95 per cent, of the world's output of all classes of diamond 
is now handled by the Diamond Corporation, sales contracts with producers 
being negotiated every five years. The latest contracts run to the end of 1960 and 



include important diamond operators in Angola, Belgian Congo, Sierra Leone, 
Tanganyika and Ghana, in addition of course to the South African producers. 

It is stated that the aim of the selling arrangements has not at any time been to 
maximize prices obtainable at any given moment, but rather to achieve a stable 
market over a period in a commodity with a speculative reputation and so ensure 
continuity of production; obtain confidence for the investment of fresh capital in 
industry, and above all to prevent a return of the desperate conditions suffered by 
the producing industry over twenty-five years ago. It is claimed that during all the 
time that these marketing arrangements have been developed there has been no 
question of any restriction of the production or of any pressure in this direction 
being placed on individual mines. 

In this connection the following figures showing the values of sales of gem and 
industrial diamonds through the Central Selling Organization of the Diamond 
Corporation Ltd. are of interest: 

£ Sterling 





. 46,780,632 



1952 . 

. 45,769,857 



1953 . 

. 43,336,109 




. 45,610,010 




. 50,253,946 




. 50,542,240 



1957 . 

. 52,818,096 



1958 . 

. 49,420,695 




. 63,033,187 



Probably about 70 per cent, of the world's production of diamonds of all 
classes is exported to the United States. 

The unit of weight employed for recording production of diamonds of all classes 
is the metric carat of 200 mg. As a rough indication of size a brilliant cut diamond 
weighing 1 carat measures about i in. across and one of 5 carats would be about 

The world's production of diamonds marketed has steadily increased during 
recent years and in 1957 totalled about 25,230,000 metric carats, of which 7,987,577 
carats came from British countries. The countries having the largest outputs (in 
carats) of diamonds (gem and industrial) in 1957 were the Belgian Congo (1 5,646,730) ; 
the Union of South Africa (2,578,975); Ghana (3,124,825); South West Africa 
(996,965); Angola (864,372); Sierra Leone (863,202); Tanganyika (390,971); French 
West Africa (247,138); Brazil (250,000); Venezuela (122,597); French Equatorial 
Africa (109,231). 

Official statistics do not always give separate returns for the production of 
industrial diamonds, but a useful compilation produced by the U.S. Bureau 
of Mines and recorded in their Annual " Minerals Yearbook," is shown in 
Table 62. 



Table 62 

World Production of Industrial Diamonds*. {1,000 carats) 

















Belgian Congo . 








French. Eq. Africa 








French West Africa 
















Sierra Leonef 








South West Africa 
















Union of SouthAfrica 

Pipe mines : 









De Beers Group 
















Alluvial mines 








S. America 









British Guiana . 
















Other countries 

Australia, Borneo, 









World Total 








* From " Minerals Yearbook," U.S. Bureau of Mines. 
t Includes unofficial production and Liberia. 
j Estimated. 

The ratio of industrial to gem diamonds recovered from deposits varies consider- 
ably as shown in the following table: 

Per cent. 
Source Industrial 

British Guiana, Alluvial gravels 18 

Ghana, Alluvial gravels ....... 50-56 

Sierra Leone, Alluvial gravels . . . .66 

Tanganyika, Kimberlite pipes and gravels .50 

Union of South Africa, Kimberlite pipes and gravels . . 80 

At the present time probably nearly 99 per cent, of the world's output of industrial 
diamonds comes from Africa. The country importing the largest amount of 
industrial diamonds in 1956 was the United States, which took 16,155,000 
carats, valued at £25,747,558; in 1957, however, the quantities had fallen to 
12,178,000 carats valued at £17,807,693. 

In industry the term bort, sometimes written boart, or bortz, is often applied to 
diamond material which is used in a crushed or fragmental form (" crushing bort ") 
and hence the term has come to be used to describe any diamonds which are un- 
suitable for use as gem stones on account of their size, colour or other imperfections. 
Some countries differentiate between various grades of bort. Thus, the United 



States import statistics divide industrial diamonds into the following categories: 
(1) carbonado, a closely knit aggregate of very small diamond crystals, and ballas, a 
globular mass of crystals; (2) diamond dust or powder; (3) crushing bort, including 
bort that has been crushed or is suitable for crushing; (4) other industrial diamonds 
not elsewhere specified, such as miners', glaziers' and engravers' diamonds, but not 
including diamond bort or manufactured diamond dies. 

Diamonds are found in two general types of deposits : (1) in complex rock masses 
consisting largely of serpentine, usually found in the form of intrusive pipes or 
dykes and known as " blue ground " or " kimberlite "; (2) in alluvial deposits. 

Kimberlite, or " blue ground," which is the rock mass in which primary diamond 
deposits occur, is a greenish blue ultrabasic rock of somewhat variable character 
and may consist of a peridotic tuff, or breccia, with a serpentinous groundmass. It 
occurs principally in funnel-shaped bodies called " pipes," which may vary in 
diameter from about 50 ft. to over half a mile. They are usually mined first by 
opencast workings and later by shafts and main haulage drifts driven into the pipe 
at regular vertical intervals. The blue ground when fresh from the mine is hard and 
compact, but soon breaks down on exposure to the atmosphere. Originally, on 
removal from the mine the rock was crushed between corrugated rolls and sub- 
mitted to a process which effected a concentration of about 100 to 1. The concen- 
trates so obtained were next sized and jigged. The process used for many years for 
the further separation of the diamonds consisted of running the jig concentrates 
over inclined oscillating sheets of galvanized iron coated with grease (petrolatum) to 
which the diamonds adhered together with some ilmenite and pyrites, the useless 
material being washed away. This concentration depends upon the fact that dia- 
mond is only wetted by water with great difficulty but is readily held by grease. In 
the more modern method the concentrates are separated into two sizes, coarse 
(+ 10-mesh) and fine (— 10-mesh), the coarse concentrate being treated by heavy 
media separation using ferro-silicon. The rejects from this treatment amount to 
about 80 per cent. The selected 20 per cent, of the material is then concentrated on 
grease tables. This grease process in slightly modified form is still in use. In all cases 
where diamonds adhere readily to grease (pipe diamonds) the vibrating grease table 
is used. This mechanism has five to eight times the capacity of the older table. The 
fine concentrates are next further treated on jigs and grease tables. The mineral 
collecting on the grease tables is scraped off and boiled to remove the grease. 
The mineral grains above ^ in. are hand sorted to remove gravel and those below 
■& in. are treated electrostatically. 

The percentage yield of diamonds naturally varies between rather wide limits, 
but it has been stated that at Kimberley a daily crushing of 5,000 tons yields about 
0-4 lb. diamonds. 

A full account of the mining practice at Kimberley is given by R. Daniel in 
Vol. LXII of " The Transactions of the Institution of Mining and Metallurgy ". 

The increasing demand for industrial diamonds has caused much attention to be 
given to methods designed to recover diamonds which normally are not adherent to 
grease and cannot therefore be recovered by the usual processes. To treat these 
diamonds two processes have been developed in the Diamond Research Laboratory. 



On irocess separates the diamonds electrostatically, the other coats the surface 

of s diamond with a water repellent substance which enables it to adhere to 

grc :. The electrostatic process is suitable for diamonds up to 6 mm. (approx. 2 

cai ), the other process works on diamonds from, say, 3 mm. to 25 mm. and 

lar . It is stated that in the Belgian Congo heavy media separation processes are 

be: installed with a view to their replacing washing processes. At the Williamson 

mi in Tanganyika in 1956, about 7,000 tons of gravel was being treated daily by a 

co ined heavy media and grease band method and the overall recovery was 

im ived and the proportion of less valuable stones obtained was greater. 

:veral years ago when the available supply of industrial diamonds seemed 

im sly to expand at the same rate as the demand, users of diamond grinding wheels 

in ; United States were urged to adopt measures for recovering diamond from 

gr ing sludges and dust, but it was stated that the operation was not likely to be 

ec >mic if the diamond content of the waste was less than one carat per pound. A 

re t on the reclamation for diamond manufacturing processes was issued in 1954 

b> e U.S. Department of Commerce. 


I the uses for industrial diamond depend upon its hardness, and abrasive 

w rties and hence its use in rock drill bits, grinding wheels and in wire-drawing 

y An estimate made by the U.S. National Research Council and shown in Table 

affords a useful indication of the relative consumption of industrial diamonds by 

^ e various trades for 1953 (later figures are not available), {see p. 179). 

The U.S. National Stockpile Purchasing Specification B-19, dated April 1st, 
1949, lists twelve classes of industrial diamonds: 

Class 1 . Core drilling stones. This class is sub-divided into four categories : 



Stones per carat 


First Quality 

. Sound, whole, round stones . ^ 



Second Quality . 

. Sound, whole, round stones . 



Third Quality 

. Sound blocks ordinarily used as 

casting boart J 

10- 3 


Congo and Sierra 

Sound, whole round stones > 

5 and under 


Round stones and cubes in 


smaller sizes 


Carats per stone 

Class 2. Thread and gear grinder stones. This class is divided into two categories : 
(a) (1) Smaller than 10 per carat, for thread grinding. 
(a) (2) 10-12 per carat, mostly for gear grinders. 



Class 3. Tool stones. This class is divided into three categories: 

(a) First quality 

(b) Second quality 

(c) Third quality 


Primarily for fine tools and any tool 
stone can be used as a dresser. 

Carats per stone 


2 00 to 400 
4 00 and 

Class 4 : Grinding wheel dressers. This class is divided into five categories : 

(a) First quality 

(6) Second quality 

(c) Third quality 

(d) Fourth quality 

(e) Fifth quality 


Grinding wheel dressers for truing abrasive 
wheels and abrasive products 



2 00 
2 00 to 400 

400 and larger. 

Class 5. Shaping, boring and turning tools. This class is divided into two 

(a) First quality . (1) 0-25 to 100 carat. (2) 100 carat and larger. 

(£») Second quality . . (1) 0-25 to 1-00 carat. (2) 1 00 carat and larger. 

Class 6. Points and elongated stones. This class is divided into four categories. 
(a) First quality whole stones 



(b) Second quality whole , 

(c) First quality cleaved stones"\ 

(d) Second quality cleaved j 

Whole stones for coning, dressing 
and radius dressing 

Cleaved stones for coning, dress- 
ing and radius dressing 

3 per carat 

1 00 and 




Class 7. Flats. This class is divided into two categories: 
Category Remarks 

(a) First quality . 

(b) Second quality 

For chisels and special tools 


3 per carat 

and smaller 

0-5 to 100 

100 and 


Class 8. Wire-die stones. This class refers to stones for wire-drawing dies and 
comprises (1) smalls; (2) stones 0-25 to 1 00 carat and (3) stones 1 00 to 200 carat. 

Class 9. Indenters. This class comprises all first quality stones for hardness 
testing, of 3 to 12 per carat. 

Class 10. Ballas. This class comprises (1) whole stones and (2) broken pieces. 

Class 11. Carbons. 

Class 12. Crushing boart. 

Table 63 

Consumption of Industrial Diamonds in the U.S.A. — by Trades 



Sharpening, milling cutters, broaches and fluted tools of cemented carbides 

Surface, cylindrical and internal grinding of cemented carbides 

Sharpening single point tools of cemented carbides 

Chip broaching, grinding of cemented carbides 

Shaping and finished dies .... 

Glass industry grinding operations 


Per cent. 






The possible synthesis of diamonds on a commercial scale has been the subject 
of researches carried on during the past fifty years, but success was only achieved 
about the year 1955 at the Laboratories of the General Electric Company at 
Schnectady, U.S.A. Full details are not available, but it is understood that the 
transformation of carbon into diamond is effected in the presence of a molten metal 
catalyst at pressures between 800,000 and 1,800,000 p.s.i. simultaneously with 
temperatures between 2,200 and 4,400°F. The catalyst metal can be either chromium, 
manganese, iron, cobalt, nickel, ruthenium, rhodium, palladium, platinum or 
osmium. The best results are obtained when using pure graphite as the carbonaceous 
starting material, but other carbonaceous materials such as carbon black sugar- 
charcoal may be used. 

By the new General Electric process new diamond can be produced whether 
seed crystals are present or not and the formation of industrial diamond of 80-mesh 



or finer is completed in a few minutes, the rate of growth being at least 01 mm. 
per minute. The shape of the synthetic diamond crystal produced varies with the 
temperature of formation, cubes predominating at the lower end of the critical 
temperature range, mixed cubes, cubo-octahedra and dodecahedra at the inter- 
mediate and octahedra at the upper limits. It has been stated that a pilot plant 
at Detroit produced over 100,000 carats during two years of operation and that 
future plans provided for an annual production of 3£ million carats by the end 
of 1958. According to information kindly supplied by the International General 
Electric Company of New York, they are producing a complete line of graded 
diamonds available in 10 grades ranging in size from + 40- to - 325-mesh. They 
state that at the present time the primary use for General Electric diamonds is in 
resinoid wheels, although in vitreous wheels they also give outstanding performance. 
The diamonds are also being used in the polishing of wire-drawing dies and are 
under trial for use in the polishing of jewel bearings. Some experimental work is also 
being carried out with another type of G. E. diamond which shows promise of 
working in metal-bonded wheels. It was expected that a product suitable for use in 
metal-bonded wheels will be available commercially during 1959. The company state 
that their industrial diamonds are being manufactured in increasing quantities and 
that generally the price is approximately 5 per cent, greater than that of natural 

Late in 1959 it was announced that the Adamant Laboratory, Johannesburg, a 
subsidiary of De Beers Consolidated Mines Ltd., had developed a process for 
making synthetic industrial diamonds of a type suitable for use in resinoid-bonded 
grinding wheels. The process used is understood to be somewhat similar to that 
devised by the General Electric Co. In May 1960 it was announced that the Norton 
Co. of Worcester, Mass., U.S.A., had produced synthetic diamonds. 

As regards substitutes, in 1957 it was announced that the General Electric 
Company of America had produced a boron nitride which they named " Borazon," 
in the form of sand grains which were harder than diamond, but the material was 
not available commercially early in 1959. 

Various processes have been devized to partially replace the diamond grinding 
wheel. These include (1) electro-discharge processes in which the stock is removed 
by sparking or arcing between the work and an electrode; a process used for shaping 
and finishing dies : (2) electrolytic grinding ; (3) ultra-sonic abrasive grinding in which 
the stock removal is effected by using a finely ground abrasive in water flowing over 
a tool vibrating at ultrasonic frequencies. 


" Abrasive and Industrial Diamonds." By P. M. Tyler. U.S. Bur. Mines. Inf. Circ, 6562, 1932, 

25 pp. 
"The Genesis of the Diamond." By A. F. Williams. Lond., 1932, 636 pp. 
" Gemstones." By G. E. Howling. Imperial Institute, Lond., 1933, 137 pp. 
" Alluvial Diamonds in South Africa." By W. E. Sinclair. Mining Mag. Lond., 1940, 62, 

" Gemstones." By G. F. H. Smith, 10th Ed. New York, 1949, 537 pp. 
" Diamond-Industrial." By H. P. Chandler. " Mineral Facts and Problems." U.S. Bur. Mines 

Bull. 585, 1960, 8 pp. 
" Diamond Mining Practice in Kimberley, South Africa." By R. Daniel. Trans. Inst. Min. Met.. 

1953, 62, 201-228. 



" Recovery of Small Diamonds." Optima, 1954, 4, 33-34. 

" Conservation of Industrial Diamonds." (Bibliography of Technical Reports), U.S. Dept. Com- 
merce, 1954, 21, (No. 4) ) 110. 

" Diamond Sludge Recovery." By F. J. Lennon. Indus. Diam. Rev., 1954, 14 (Jan.), 18-19. 

" Recovery of Small Diamonds," Mining and Indus. Mag., 1954, 44, 119. 

" Quality — The Key to Economical Use of Diamond Abrasives." By C. B. Myer. Indus. Diam. 
Rev., 1954, 14 (Oct.), 209-210. 

" The Diamond Industry." By A. Moyar, J. K. Smit & Sons, Lond., 69 pp. 

" Diamond Technology." By. P. Grodzinski, N.A.G. Press, Lond., 2nd Ed. 1953, 784 pp. 

" The Principle and Design of a Nuclear Radiation Counter which uses a Diamond as its Detec- 
tor." By F. W. Cotty. Indus. Diam. Rev., 1956, 16, 12. 

" Baceka's Industrial Mining Operations at Bakwanga." By T. G. Murdock. U.S. Bur. Mines, 
Mineral Trade Notes, 1955, 40, No. 6, 23 pp. 

" The Making of Synthetic Diamonds." Chem. andlnd., 1959 (Dec. 5th), 1538-9. 

" The Preparation of Diamond." By H. P. Bovenkirk, F. P. Bundy, H. T. Hale, H. M. Strong 
and R. H. Wentorf. Nature, 1959, 184, 1094-8. 

" Gem Stones and Allied Materials." By R. H. Jahns. " Industrial Minerals and Rocks." Amer. 
Inst. Met. and Petrol. Engnrs.. New York, 1960, 3rd Ed., pp. 383-441. 

" Synthetic and Other Man-made Gems " (diamond, ruby, sapphire, spinel, strontium titanate). 
By R. J. Holmes, Foote-Prints, 1960, 32, No. 1, 3-24. 

" Abrasive Materials." U.S. Bur. Mines. Minerals Yearbook (Annual). 

" Bibliography of Industrial Diamond Applications " (Monthly). Industrial Diamond Informa- 
tion Bureau, London. 


U.S. National Stockpile Specification: 

Industrial Diamonds, P-19, April 1st, 1949, 

Diatomaceous Earth 

Diatomaceous earth, which is known under numerous designations, such as 
diatomite, kieselguhr, tripolite, fossil flour, etc., 'is also sold under various trade 
names. It consists of the siliceous remains of microscopic aquatic organisms known 
as diatoms. Individual diatoms may vary in length from 0005 to 0-4 mm. 

World Production 

Diatomite occurs and is mined in many countries, but statistics of production 
for recent years are very incomplete — no returns being available for Hungary, 
Norway, Portugal, Roumania, Spain, the U.S.S.R., Brazil, Japan and Korea, all of 
which are known to be producing. Countries for which statistics of production are 
ivailable in order of importance are: United States, Denmark, France, Federal 
-Jermany, Great Britain, Italy, Algeria, Northern Ireland, Australia, Costa Rica 
and Kenya. The world's production in 1958 was estimated to amount to about 
736,000 long tons. The United Kingdom's production in 1958 amounted to 25,138 
long tons. Imports in 1958 totalled 59,562 long tons, a large proportion of which 
came from Denmark. 

The world's largest and purest deposits of diatomite are probably those occur- 
ring in the United States in the Lompoc area, 50 miles north-west of Santa Barbara, 
California, operated by the Great Lakes Carbon Corporation and the Johns- 



Manville Company. The deposit operated by the last-named company covers an 
area of between 3 and 4 square miles and extends to an average depth of 700 ft., 
overlain by varying depths of overburden. 

Preparation for the Market 

The purest form of diatomaceous earth is composed chiefly of opaline silica, 
but in most commercial deposits the material contains impurities, such as quartz 
sand, clay, iron oxide, carbonates of lime and magnesia, organic or carbonaceous 
matter and water, so that the content of diatomaceous silica rarely exceeds 85 per 

A concise account of diatomite mining and processing, as carried out in 
California, has been given by W. Q. Hull (1953). 

Diatomite is marketed in three general forms, i.e. natural, calcined and flux- 
calcined. The natural product has been dried, ground and if necessary air classified. 
The calcined product has been heated to a fairly high temperature to remove 
moisture and organic matter, and air classified. Calcination results in a change in 
the filtration properties of the diatomite, some impurities being converted to fused 
slags, such as aluminium silicate, which are later removed. 

The flux-calcined, or " white," product is obtained by adding from 3 to 10 per 
cent, by weight of an alkali salt, usually soda ash, and calcining in a rotary kiln. The 
feed temperature employed is about 300-400°F. and the maximum temperature at 
discharge is about 2,200°F. The effect of this treatment is to increase the amount of 
" melting " on the surface of the diatomite particles and so make them more 
suitable for filtration purposes. 


The many uses for diatomite include the following: (a) as a filtering agent in the 
clarification of sugar, fruit juices and oils; Q>) in heat and sound insulation, in the 
form of bricks or loose powder; (c) as a porous extender and flatting agent in 
certain paints; (d) as a dusting agent to prevent the caking of fertilizers containing 
ammonium nitrate; and (e) as a filler in light-weight concrete, rubber goods and 

As a rough guide to the proportions used by various industries, it may be stated 
that, of the total consumption in the United States, about half is used for filtration, 
one quarter in fillers, and the remainder for various purposes, such as insulation, 
abrasives, absorbents, in herbicides, for making sodium and calcium silicates and 
in concrete admixtures, paint, paper, etc. 

Filtration. Specially selected and processed diatomite is often employed as a 
filter-aid for the removal of slimy, non-rigid or colloidal matter from suspensions 
(particularly in oils, sugar syrups, glucose, etc.), which could not be clarified by 
ordinary filtration. The addition of a small percentage of a selected, suitably 
processed diatomite ensures the formation on the filter cloth of an open porous 
cake which traps all suspended matter, increases the rate of flow and produces a 
clear filtrate. The amount of filter aid added varies between 01 and 0-5 per cent, of 
the weight of liquid to be treated. The suitability of a diatomite for the filtration of 



a particular product can only be ascertained by practical trials, but as a general rule 
it can be stated that freedom from carbonates, clay, iron oxide and organic matter 
is desirable. 

Such filter aids have been used in the sugar industry for over thirty-five years. 
They may be used either by incorporating them with the liquid to be treated, 
depositing them on the filter cloth or by a combination of the two methods. 

The value of diatomite for filtration purposes depends upon the type of diatoms 
present, their size and shape, and relative freedom from small broken material. 

Carbonates of lime and magnesia are objectionable in diatomite intended for the 
nitration of acid liquors, such as lemon juice, but not in the case of neutral liquors, 
which do not dissolve the carbonates. Clay is a most undesirable impurity on account 
of its tendency to produce a slime and 6 per cent, is the maximum amount usually 
permissible. Occasionally a limit of 1 per cent, is put on the iron oxide content. 

Sodium chloride may be present in some raw diatomites up to 10 per cent., but 
more than a few tenths per cent, is objectionable, as the salt may dissolve into the 
liquor being filtered. 

During World War II, diatomite filters were used by British and United States 
forces for water treatment, particularly for removing amoebic cysts and blood 
fluke lavs. Diatomite filter aids are used in the pressure filtration of public water 
supplies in four towns in New York State. Diatomite niters have also been used for 
industrial purposes, such as the removal of small quantities of organic matter from 
solutions, the clarification of copper plating solutions, filtering magnesium bicar- 
bonate solutions and those containing ferrous sulphide. 

The Johns-Manville Company market twelve standard grades of their " Celite " 
filter-aid to cover the requirements of industry generally and these are supple- 
mented by some twelve special grades. A typical chemical analysis of the product 
is shown in Table 64. 

Filter-aids made by the Great Lakes Carbon Corporation and marketed under 
the trade name " Dicalite " are sold in Great Britain by F. W. Berk & Co. of 
London. Ten grades of product are available, varying in properties according to 
the nature and size of the particles to be removed and the relative rate of flow 
required in either vacuum or pressure filtration. 

Diatomite produced in France and North Africa, and prepared by the Societe 
Ceca, is marketed in Great Britain as filter aids by the British Ceca Company Ltd . of 
London, under the name of " Clarcel." Eight grades of the prepared diatomite are 
available, varying considerably in their nitration rates and clarifying power. The 
quantity of diatomite required varies from 05 to 0-30 per cent, of the weight of 
liquid to be treated and its nature. Interesting information concerning methods of 
using these filter aids in the preparation of a wide range of products, such as bever- 
ages, sugars, vegetable and mineral oils, pharmaceutical products, varnishes and 
dry-cleaning solvents will be found in the leaflets issued by the Johns-Manville 
Company, the Great Lakes Carbon Corporation, and the British Ceca Company. 

Filter aids prepared from German diatomite by the Kieselguhr-Industrie G.m.b.H . 
are marketed in Great Britain by Charles H. Windschuegl Ltd. of London. The 
products, which have all been calcined and ground, are mostly off-white in colour. 



The chemical composition of several brands of diatomite filter-aids marketed 
in Great Britain is shown in Table 64. It is understood that the nature of the 
diatoms in the French and German products differs considerably from those 
occurring in American diatomite. 

Table 64 

Composition of some Diatomite Filter Aids 

Per cent. 


Great Lakes 

British Ceca 


Carbon Corp. 

Co. Ltd. 


" Dicalite " 

" Clarcel 





Silica, SiO a 





Alumina, Al 2 O s . 





Ferric oxide, Fea0 3 





Titanium dioxide, TiO s 




Lime, CaO 



}" 5 


Magnesia, MgO . 




Soda, NaaO 

\ 3-3 


| 9-0 


Potash, K a O 



Water soluble matter . 


Moisture . 





Loss on ignition . 





* By difference. 

Insulation. Diatomite is suitable for both high and low temperature insulation. 
For heat and sound insulation the most important factors are its weight per cubic 
foot and thermal conductivity. 

The diatomite may be supplied either in the form of bricks or blocks as cut from 
the deposit and dried, crushed aggregate or fine powder. The bricks may be cut in the 
quarry like building stone, dried or calcined in kilns and trimmed to shape, or 
produced from the powdered mineral by pressing moist, with or without the addition 
of a bonding material, such as clay. Powdered diatomite may be used for insulation 
in the form of a loose fill. 

Figures naturally vary for diatomites from different sources, but as a rough 
average it may be stated that good quality powdered diatomite for insulation pur- 
poses weighs about 10 lb. per cu. ft. and has a thermal conductivity from 0-3 to 0-5. 
The weight per cubic foot of diatomite bricks or blocks is about 28 lb. and their 
thermal conductivity varies from about 0-6 at ordinary temperatures up to 11 at 
1,200° C. 

A.S.T.M. Specification C 197-48 covers diatomaceous silica thermal insulating 
material in the form of dry cement or plaster, intended to be mixed with a suitable 
proportion of water, applied as a plastic mass, and dried in place, for use as insula- 
tion on surfaces operating at temperatures between 100 and 1,900° F. The cement 
shall be composed predominantly, by weight, of diatomaceous silica with suitable 
proportion of heat-resisting binder. The specification requires the material to con- 
form to limits provided in regard to storage density, dry covering capacity, volume 



change (shrinkage upon drying) and thermal conductivity at 200, 500 and 700° F. 
Diatomaceous earth thermal insulation for pipes is dealt with in A.S.T.M. Specific- 
ation C 334-54T. 

Denmark produces and exports large quantities of an impure diatomite which 
contains a fairly large proportion of clay and is termed moler. The output amounts 
to about 70,000 tons annually. Much of the moler is moulded into bricks and slabs 
and burnt like ordinary clay. Calcined moler products have certain advantages for 
use in building construction owing to their good heat resisting and sound insulating 
properties, combined with strength and light weight. The calcined moler may contain 
up to 75 per cent. SiC>2, about one-third being in the form of quartz. 

Catalyst Carriers. For many years diatomite in the form of powder has been 
used as a support for a number of catalysts, notably nickel and vanadium, and more 
recently the mineral has been available in the form of granules, pellets and a variety 
of pre-formed shapes. Two such catalyst carriers, " Celite " 408 and 410, made by the 
Johns-Manville Company are stated to be finding much use in the petro-chemical 
industry. The carriers are claimed to combine high absorption, porosity and strength 
with low density and a large surface area. For example, " Celite 410 " has a cold 
water absorption of 58 per cent, by weight, a compressive strength of 3,200 p.s.i. 
and a surface area of 2-4 sq. m. per gm. (liquid nitrogen absorption). It is stated to 
be able to withstand temperatures up to about 2,000-2,300° F. 

Paint. Diatomite is finding increasing use in this country and in the United 
States as a constituent of paint. Its main functions are as a porous extender for 
inside flat wall paints and primers, and as a flatting agent in certain enamels and 
lacquers. It has a high oil absorption and a low gloss, and is rather difficult to 
grind. The addition of diatomite is claimed to increase adhesion and to minimize 
any tendency towards blistering and chalking. The inclusion of suitably prepared 
diatomite in traffic paint is said to give increased night-visibility. 

The percentage chemical composition of one diatomite so used is stated to be as 
follows: Si0 2 , 86-2; AI2O3, 305; Fe 2 3 , 102; CaO, 018; MgO, 0-65; H2O, 5-6; and 
CO2 and organic matter, 1 -20. 

British Standard Specification B.S. 1795 : 1952 requires that diatomite for use in 
paints shall contain not less than 90 per cent, of matter insoluble in hydrochloric 
acid, calculated on the material after drying at 98°-102°C. The loss on ignition at 
900° C. must not exceed 8 per cent.; the iron oxide content, 0-5 per cent.; loss at 
98°-102°C, 5 per cent., and matter soluble in water, 1 per cent. The acidity or 
alkalinity of the aqueous extract is limited to 01 per cent., calculated as H2SO4, 
or Na2C03, calculated on the material. The minimum content of silica is 80 
per cent. 

The A.S.T.M. Specification D 604-42 for diatomaceous earth for use in pigments 
recognizes two grades; (a) standard fine material for general paint use in which the 
coarse particles (over 40 microns) may vary between 5 and 15 per cent., and (6) 
extra fine for special uses which may have a maximum of 1 per cent, of coarse 

For both types the following permissible maximum percentages are stipulated: 
loss on ignition, 1 ; matter soluble in 1 : 2 hydrochloric acid, 3 ; and volatile matter, 



1 . The volume of pigment settling in petroleum spirit after one hour, min. ml. is 
35 for type (a) and 25 for type (b). 

Other Uses. In recent years diatomite has been used as a dusting agent to prevent 
ammonium nitrate fertilizers from caking and to ensure even spreading. For this 
purpose a higly porous uncalcined diatomite is required, ground to 325-mesh and 
containing less than 5 per cent, of moisture. 

Diatomite has been used in ceramic glazes as a source of silica in substitution for 
flint, to which it is claimed to be superior. One diatomite stated to be suitable 
contains Si02, 91 per cent. ; AI2O3, 1 -3 per cent. ; and FeO, 2 per cent. 

Diatomite is employed to some extent in rubber mixings, but for this purpose 
must not contain more than mere traces of copper or manganese and a low percentage 
of iron oxide. One specification requires that the material, after drying, should 
contain not less than 80 per cent. Si02 and that the total of CaO, Fe203 and AI2O3 
should not exceed 3 per cent, calculated on the dry product. The loss on ignition 
must not exceed 12 per cent, and the matter retained on a 200-mesh sieve must not 
exceed 2 per cent. 

The mineral has been used in paper making as a filler, or bulking agent, in 
chip board and other cylinder machine products, and also for pitch control in over- 
coming stickiness in waste paper recovery. 

Synthetic Calcium Silicate. Diatomite is used as a basis for the manufacture of a 
synthetic calcium silicate marketed by the Johns- Manville Company under the name 
" Micro-Cel " in America and as " Calfio " in Europe. The percentage chemical 
composition for the product is: CaO, 25-3; Si0 2 , 51-7; A1 2 3 , 1-8; Fe a 8 , 0-9; 
alkalis, 0-5; loss on ignition at 1,800° F., 18 0. It will absorb from two to four times 
its weight of liquid and still remain a free-flowing powder and so permits the 
conversion of an active liquid, such as an insecticide, to powder form with a 
minimum of inert carrier. 

It is supplied in a number of grades varying in physical properties between the 
following limits : 

Colour white to off-white 

Loose-weight density 

Oil absorption 

Water absorption 

Average particle size 

pH . 

Refractive index 

Retained on 325-mesh sieve, max. 

4-5-14-5 lb./cu. ft. 

220-490 per cent, by weight 

240-560 per cent, by weight 

02-0 07 microns 



1-0-8-0 per cent. 

The product is stated to be suitable for use as a pigment extender or flatting agent 
in paints, as an anti-caking agent for ammonium nitrate or urea fertilizers, as a 
grinding aid for heat-sensitive or low-melting point solids, as a suspending aid, for 
decolorizing liquids and as a desiccant. 

Air-floated diatomite has been used for a number of years as a constituent of 
certain car polishes. One manufacturer in London requires a diatomite light grey in 
colour, having an average particle size of 1-2 microns and leaving a residue not 




exceeding 0-5 per cent, on a 325-mesh sieve. The free moisture content must not 
exceed 6 per cent, and the oil and water absorptions should average about 185 and 
210 respectively. Three varieties of prepared diatomite marketed by the Great 
Lakes Carbon Corporation under the brand marks " White Filler," " 105 " and 
" P.S.," recommended for use in car polishes, conform in general to these require- 

Possibly the oldest industrial use for diatomite is as a nitroglycerine absorbent 
in the manufacture of dynamite and, although it has been largely superseded for this 
purpose by other materials, it is still employed as an absorbent for other liquids. 

Diatomite is one of the three principal mineral fillers used in the manufacture of 
plastics, probably ranking after asbestos and mica. Its use is stated to improve the 
surface finish and to modify certain other properties, such as flow, shrinkage and 
water resistance. 


' Diatomaceous Earth." Anon. Min. Indus, of Br. Empire and Foreign Countries, Imperial 

Institute, Lond., 1928, 55 pp., including bibliography. 
' Diatomite: Its Occurrence, Preparation and Uses." By V. L. Eardley-Wilmot. Canad. Dept. 

Mines, Bull. No. 691, 1928, 182 pp. 
' Diatomaceous Earth." By R. Calvert. Amer. Chem. Soc. Mon. No. 52, New York, 1930, 256 pp. 
' Diatomite." By P. Hatmaker. U.S. Bur. Mines, Inform. Circ. No. 6391, 1931, 20 pp. 
' The Use of Chlorinated Rubber and Diatomaceous Silica in Road Paints." By H. C. Bryson. 

Paint Tech., 1940, 5 (No. 52), 86-7. 
' Extender Pigments in Exterior House Paint Formulations." By R. E. Parry and J. W. Planka. 

Am. Paint J., 1940, 24 (No. 46), 54-62. 
Diatomaceous Earth Base for Chemical Pigments." By E. C. Burwell. Industr. Engng. Chem., 

1941, 33, 915-8. 
'The Mining and Refining of Diatomite." Anon. Chem. Met. Engng., 1942 (Aug.), 110-18 

(includes flow sheets). 
' Diatomaceous Silica and Its Applications in the Paint Industry." By H. W. Hall. Paint, Oil and 

Chem. Review, 1942, 104, 7-12. 
Diatomaceous Earth." By C. J. O'Neil and R. E. Parry. " Protective and Decorative Coatings." 

Ed. by J. J. Mattiello. Lond., 1942. Vol. 2, pp. 468-79. 
' Diatomaceous Filter Aids." By A. S. Elsenbast and D. C. Morriss. Ind. Eng. Chem., 1942, 34 

(No. 4), 412-8. 
Note on the Use of Diatomite as a Source of Silica in Ceramic Glazes." By W. P. Keith. Bull. 

Amer. Ceram. Soc, 1943, 22, 373. 
Natural Mineral Paint Extenders." By C. L. Harness. U.S. Bur. Mines, Inform. Circ. No. 7264, 

1943, 19 pp. (Diatomite, pp. 12-4.) 
' Industrial Insulation with Mineral Products." By O. Bowles. U.S. Bur. Mines, Inform. Circ. 

No. 7263, 1943, 17 pp. (Diatomite, pp. 13-6.) 
' Diatomite of the North-west Pacific Coast as Filter Aids." By K. G. Skinner and others. U.S. 

Bur. Mines, Bull. 460, 1944, 87 pp. 
' Use of Fillers for Phenolics." By D. Lawrence. Modern Plastics, 1947, 25, 127-32. 
' Kieselguhrs (Suitability as Carriers for Catalysts)." By R. B. Anderson, J. T. McCarthy, W. K. 

Hall and L. J. E. Hoffer. Industr. Engng. Chem., 1947, 39, 1618-28. 
' Industrial Applications of Diatomite Filters." By E. J. Dominick. Industr. Engng. Chem., 1947, 

39, 1413-9. 
Non-metallic Minerals." By R. B. Ladoo and W. M. Myers. New York, 1951. (Diatomite, 

pp. 185-93, including bibliography.) 
Diatomite as an Abrasive for Cleaners and Polishes for Automobiles." By L. E. Weymouth and 

P. A. Martinson. Soap and Sanitary Chemicals, 1954, 30, No. 2, 139, 141, 143, 145, 175. 
' Diatomaceous Earth." By W. Q. Hull, H. Keel, J. Kenney and B. W. Gamson. Indus, and 

Eng. Chem., 1953, Feb., 256-269. 
' Diatomaceous Earth Filtration in New York State." By J. K. Fraser. /. Amer. Waterworks Ass., 

1954, 46, No. 2, 151-155. 
' Synthetic Silicates from Diatomite and Lime." By M. L. Griggs. Rock Products, 1956, 59, 

86-89 and 92. 
Celite Filter Aids." Johns-Manville Co. Ltd., London, 1956, 11 pp. 
Pigment Extenders, Flatting Agents and Filter Aids for the Finishes Industry." [A collection 

of formulations.] Johns-Manville Co. Ltd., London, 1957, 50 pp. 



" Dicalite Materials in Paper and Pulp Mills." Great Lakes Carbon Corp., N.Y., 1960, 9 pp. 
"Filtration with Dicalite Filter Aids." Technical Services Bulletin B.13, Great Lakes Carbon 

Corp., N.Y., 20 pp. 
" Celite Filter Aids and Mineral Fillers." Johns-Manville Co. Ltd., London, 22 pp. 
" Dicalite Diatomaceous Aids for Paint Manufacturers." Great Lakes Carbon Corp., N.Y 

Technical Services Bulletin C 23, 13 pp. 
" Filter Aids and Mineral Fillers." D. S. Series 450, Johns-Manville Co. Ltd., New York, 1958, 

22 pp. 
Diatomite." By A. B. Cummins. " Industrial Minerals and Rocks." 3rd Ed. Amer. Inst. Min. 

Met. Eng., 1960, pp. 303-319. 
"Diatomite." By L. M. Otis. " Mineral Facts and Problems." U.S. Bur. Mines Bull. 585, 1960, 

7 pp. 
Diatomite." U.S. Bur. Mines, Minerals Yearbook (Annual). 
" Micro-Cel Synthetic Calcium Silicate." Technical Bulletins, Celite Division, Johns-Manville t 

Co. Ltd., New York and London, 1955-58. * 

" Ceca Filter Aids." British Ceca Co., London, 12 pp. 


American Society for Testing Materials 
A.S.T.M. Standards, 1958: 

Diatomaceous Silica Thermal Insulating Cement. C 197-48. 

Diatomaceous Silica Pigment. D 604-42. 

Diatomaceous Earth, Thermal Insulation for Pipes. C 334-54T. 

British Standards Institution : 

Extenders for Paints. B.S. 1795 : 1952. 


Felspar is not the name of a specific mineral but is the term used in mineralogy to 
designate a group of rock-forming minerals, all of which consist of anhydrous 
silicates of aluminium with some potash, soda or lime. Felspars are classified into 
two chief groups: potash felspars and soda-lime felspars. 

Almost all igneous rocks contain felspar, potash felspars being less common than 
the soda variety, but only under certain favourable conditions do crystals of felspar 
occur in sufficient quantity and size to be commercially workable. 

Large quantities of Cornish-stone are produced in Great Britain and used in 
ceramic ware. In the United States and Canada nepheline-syenite is also used as a 
substitute for felspar. 

The chief felspars of commerce are: (1) potash felspar (K2O.AI2O3.6 SiOa), 
including microcline and orthoclase, which differ only in their form of crystallization; 
(2) the soda felspar, albite (Na20. AI2O3. 6 SiCfe); (3) soda-lime felspars, notably 
oligoclase and labradorite, which contain a mixture of soda and lime as well as 
alumina. Commercial felspar as marketed often contains some free quartz, possibly 
up to 20 per cent. 

The chemical composition of selected felspar crystals rarely agrees with their 
theoretical molecular formulae, as soda and potash often partially replace one 
another, as shown by the analyses given in Table 65. 

Most of the felspar of commerce is either orthoclase or microcline. 

Commercial felspar deposits often occur in pegmatites which usually carry 



Table 65 

Analyses of Some Felspars 





Silica, SiO z . 
Alumina, A1 2 3 . 
Ferric oxide, Fea0 3 
Potash, K a O . 
Soda, Na 2 . 
Lime, CaO . 
Magnesia, MgO 







22 00 


Totals . 





> certain accessory minerals that have to be separated from the felspar before sale. Of 
these minerals muscovite mica is perhaps the most common, but it can be separated 
fairly easily. 

Garnet often occurs; magnetite when present in finely disseminated form is 
difficult to remove. Both are objectionable in felspar for ceramic purposes. Biotite 
(black) mica is uncommon, but when present may be difficult to separate from the 
felspar. There is only a very limited market for felspar contaminated with iron- 
bearing minerals. Most European producers of felspar ship the unground mineral 
to wet-grinding mills in the consuming countries. In the United States, however, it 
is more usual for the grinding to be done at, or near, the mine. Froth flotation is 
used in the United States for improving the grade and recovery of felspar, about 
50 per cent, of the output being obtained by this process. Electrostatic separation 
is also used, but to a less extent. 

Cornish-stone, which is an altered granite and consists essentially of kaolinized 
potash felspar, is marketed in several grades designated as hard purple, mild purple, 
dry white and buff stone. Typical samples show the following mineralogical com- 




Purple .... 
Bufl . 

Per cent. 



Per cent. 


Per cent. 

Chemical analyses of the several grades marketed are shown in Table 66. 

The so-called " Carolina Stone " which is marketed in the United States as a 
substitute for Cornish-stone is a synthetic mixture of kaolin, felspar, quartz and a 
little fluorspar. 

Nepheline-syenite is a quartz-free rock consisting essentially of the felspathoid 
mineral nephelite (a silicate of aluminium, sodium and potassium, theoretically 
containing K2O, 7 per cent.; Na20, 15 per cent.; and AI2O3, 33 per cent.), with 
albite and microcline felspars. Accessory minerals are black mica, magnetite, 



Table 66 

Analyses of Cornish-Stone 

Per cent. 







Hard purple 

Buff .... 

Dry white . 








zircon, corundum, etc. It contains from 20-50 per cent, of combined alumina and 
17-20 per cent, of felspar. 

Nepheline-syenite, first introduced in 1940 for use in the manufacture of glass, 
particularly containers where high alumina content is required, was later employed 
also as a vitrifying agent in whiteware and sanitary ware and as a source of alumina 
and alkalis in glazes and porcelain enamels. It is also used as a bond in abrasive 
grinding wheels. In Canada separate grades are marketed for use in the glass and 
pottery industries. 

It replaces felspar for various ceramic purposes and in glass manufacture, in both 
of which its lower fusing point, higher content of alumina and absence of free 
quartz are an advantage. 

The Canadian raw material, which is obtained largely from deposits near Lake- 
field, Ontario, before being marketed is usually crushed to 20-mesh and submitted 
to magnetic separation in order to remove minerals containing iron. 

Nepheline-syenite has piezo-electric properties, but is not used for this purpose 
as the crystals are usually small and imperfect. 

It was reported in 1957 that the Volkhov Aluminium Works near Leningrad, 
U.S.S.R., were using nepheline syenite from the Kola Peninsula in place of bauxite 
as a raw material for alumina production. 

Other Felspathic Materials. In recent years there has been an increasing produc- 
tion and use in the United States of aplite as a cheap source of alkali and alumina for 
glass making. Aplite, which is mined in Virginia, consists chiefly of the felspar albite, 
the minerals zoisite and sericite, with smaller amounts of sphene, microcline and 
quartz. The product marketed contains about 60 per cent, silica, 24 per cent, alu- 
mina, 2-5 per cent, potash, 6-3 per cent, soda, 5-6 per cent, lime and 0-25 per cent, 
iron oxide. 

In 1957 the entire output was used by the glass industry. Japan has extensive 
resources of aplite and in 1957 produced 46,563 short tons, all used in the glass 

World Production 

The world's recorded production of felspar and Cornish-stone totalled about 
1,100,000 long tons in 1958, excluding felspar known to have been produced in 
Czechoslovakia, Roumania, the U.S.S.R. and Brazil. The largest recorded outputs 
were made in the United States, Federal Germany, France, Great Britain, Italy, 



Norway, Sweden and Japan. The production of nepheline-syenite in Canada, not 
included in the above world's total, has increased annually for some years and in 
1958 totalled 179,737 long tons. Great Britain in 1958 produced 47,826 long tons 
of Cornish- or china-stone and imported 29,323 long tons of felspar. 


Felspar is used principally in the manufacture of glass, pottery, vitrified enamels 
and special electrical porcelain. Less important uses include its employment as a 
flux or binding agent; in certain scouring soaps and in artificial teeth. Low-grade 
crushed felspar is used in the U.S.A. for surfacing prepared roofing material, for 
stucco and facing cement blocks, as poultry grit and for sand blast work. The 
consumption of ground felspar in the United States for various purposes is shown 
in Table 67. 

Table 67 

Ground Felspar sold by Merchant Mills in the U.S.A.* 
Per cent, of total 








Other uses, including soap and abrasives 



















Total tonnage, (short tons) . 






* Excluding nepheline-syenite, aplite and other sources of alumina used in glassmaking. 
From " Minerals Yearbook," U.S. Bur. Mines. 

In 1958, the above total was made up as follows: hand sorted, 177,434; flotation 
concentrates, 232,606; felspathic sands, 59,472, short tons respectively. The largest 
use for hand-sorted felspar and flotation concentrates was in glass manufacture; a 
large proportion of the felspathic sands was used in pottery. 

Several attempts have been made in the U.S.A. by the National Bureau of 
Standards, the Feldspar Association and others, to formulate standard specific- 
ations for felspar products offered to industry, but apparently no specification has 
yet found general acceptance. 

In 1930, the National Bureau of Standards issued a specification " Feldspar 
CS 23-30 " for ground felspar for use in ceramic products which had the assent of 
many important producers and users. It was intended as a classification rather than 
a definite purchase specification, and was based on chemical composition and 
particle size. The following three groups were designated: 

(1) Commonly accepted ceramic or body grades, based on silica content and 
ratio of potash to soda, and containing less than 4 per cent. Na20. The grades 
covered a range of silica content between 64 and 73-99 per cent, and ratios of 
6 K2O : 1 NaaO downwards to 3 parts or less K2O : 1 Na20. 

(2) This group included felspars used chiefly in ceramic glazes and provided for 
grades containing 4 per cent, or over of Na20. 



(3) This group covered felspar used for glass-making and was based on content 
of silica, alumina and iron. The grades covered Si02 contents between 64 and 71 -99 
per cent., AI2O3, 15-19-99 per cent., and maxima for Fe203 ranging from 015 to 
over 0-2 per cent. 

In 1935, the National Feldspar Association published a rather less involved 
classification, based more upon uses than on chemical analysis, and eliminated the 
alkali ratio. 

Glassmaking. Felspar, which may constitute from 10 to 50 per cent, of the batch, 
may be added to provide alumina or alkalis, the higher percentages being used for 
the best quality white glassware. If alumina is the chief consideration then soda 
felspar containing not less than 20 per cent. AI2O3 is preferred as its content is 
almost invariably higher than that of potash felspar. In some cases, however, the 
use of potash felspars may be desirable owing to their lower percentage of iron. 

The chemical composition of some felspars and nepheline-syenite used in glass- 
making is shown in Table 68. 

Table 68 

Composition of Commercial Felspars for Glassmaking. 
Per cent. 

Potash felspars 

Soda felspars 










SiO a . 









A1 2 0, 

15 3 








CaO . 









K s O . 








5 04 

Na a O. 









Fe 2 0, 









Loss . 









Nos. 1, 2, 4, 5, and 6 were from Scandinavia, Nos. 3 and 7, from U.S.A., No. 8 
from Canada. 

It is generally considered that for use in making the highest-class colourless glass, 
felspar should not contain more than 0-1 per cent, iron oxide, and that for most 
varieties of colourless hollow-ware the limit is about 0-3 per cent. These limits make 
it desirable that every effort should be made during the dressing of the felspar to 
remove iron-bearing minerals such as pyrite, limonite, magnetite, garnet, tour- 
maline, biotite, and hornblende. The mode of occurrence of the iron in ground 
felspar is important; iron in the form of black specks is most undesirable but less so 
if it is evenly distributed throughout the felspar. Titanium, which may occur in the 
form of ilmenite, is also objectionable. Organic matter should be as low as possible, 
a good indication of its presence being given by the loss on ignition of the air-dried 
sample, which should not exceed about 1 per cent. 

In the United States two grades of felspar for glassmaking are commonly 
marketed, i.e. (1 ) with less than 6 per cent, of free quartz, and lime (CaO) not exceed- 



ing 2 per cent., and (2) carrying not less than 17 per cent, alumina (AI2O3) with 
alkalis (Na20 plus K2O) not under 11-5 per cent., and iron oxide (Fe2C>3) not over 
01 per cent. 

Glassmakers' requirements concerning the fineness and grading of ground 
felspar supplied to them range between about 20 and 200-mesh. Some users claim that 
material finer than 80-mesh is undesirable as it tends to ball up in the glass furnace. 

Two samples of ground felspar, stated to be suitable for use in English tank 
furnaces, had the following screen analyses : 

B.S.I. Sieve 

Sample A 

Sample B 

On 52-mesh 

Through 52 on 72-mesh . 
72 „ 100 „ . 
100 „ 120 „ . . . 
,,120 .... 

Per cent. 






Per cent. 


In general the ground felspar, as delivered to the consumer, should all pass a 
36 B.S.I, sieve and the bulk should pass a 100-mesh sieve. 

In the United States the usual limits are that all material should pass a 20-mesh 
sieve and that very little shall be finer than 200-mesh. One producer is marketing 
three grades: (1) containing 42-65 per cent, retained on 200-mesh; (2) 65-85 per 
cent, on 200-mesh; and (3) 85 per cent, and over on 200-mesh. On the other hand, 
however, some users are employing a product of which 36 per cent, passes 200-mesh. 

Ceramics. In the ceramic industry felspar and nepheline-syenite are used both 
in the body and as a glaze for chinaware. The dressed felspar should be free from the 
mineral impurities mentioned above under " Glassmaking." 

Potash felspar sold for pottery purposes in Great Britain is usually required to 
contain not less than 8 per cent. K2O, preferably over 10 per cent. The content of 
soda should be low, say, not more than 2 per cent. For the best quality ware free 
quartz should not be over 5 per cent., but for lower quality products as much as 
20 per cent, may be permissible. The iron content should be low (in the best grades it 
is below 01 per cent.) and lime should not exceed 0-5 per cent. When calcined, the 
felspar should give a frit of uniform colour and free from spots or specks. 

In the United States three grades of felspar for use in ceramics are commonly 
recognized; No. 1 spar, which is practically free from quartz; No. 2 spar, containing 
not over 25 per cent, of free silica; and No. 3 spar, containing not over 30 per cent, 
of free silica. The colours of Nos. 1 and 2 may vary from brownish to clear white, 
but the mineral should be free from specks. Important factors for such material are 
its behaviour on fusion, fusion temperature and shrinkage on firing in porcelain 
body mixtures. 

In recent years there has been an increasing use of nepheline-syenite in place of 
felspar in sanitary, wall and floor tiles, in electrical porcelain and in semi-vitrified 
bodies. It is claimed to require a lower firing temperature and to give an increased 
firing range. 



The consumption of nepheline syenite in the United States rose from 95,782 
short tons in 1954 to 164,782 short tons in 1958, practically all imported from 
Canada for use in the glass industry. 

Felspar for use in glaze mixtures should not usually contain more than 0-1 per 
cent, of iron oxide (Fe203) and must yield a clear transparent product on fusion. Its 
colour before fusion should be white, or slightly pink. The pink colour may be due 
to manganese, which may help to reduce the chromatic effect in the finished glaze 
due to iron oxide. It has been stated that orthoclase felspar, with its high content 
of silica and alumina, does not always yield a clear glaze on cooling and that alkali- 
lime silicates are to be preferred. 

Vitreous Enamels. Felspar is an important constituent in many enamels used for 
coating metal ware. A rather coarser grade than that used for chinaware is usually 
required — say most of the mineral to pass 20-mesh and be retained on an 80-mesh 
sieve, with only a small proportion of fine particles. For white enamels a low content 
of iron oxide is required, with possibly 0-5 per cent, as the higher limit. 

Other uses. Felspar is used as a bonding agent or flux for carborundum and emery 
abrasive wheels and for this purpose is often sold ready ground to pass a 200-mesh 

For the manufacture of artificial teeth only the highest quality pure white potash 
felspar is employed, the proportion used being about 80 per cent, of the mixture. A 
typical analysis of a dental felspar shows the following percentage composition: 
Si0 2 , 65-6; AI2O3, 18-7; K 2 0, 12-5; Na 2 0, 2-5; CaO, 0-4; Fe 2 3 , 007; MgO, trace; 
loss on ignition, 0-5. 

Felspar is a constituent of certain scouring soaps and for this purpose should be 
free from quartz grit, but may contain rather more mica than is permissible in 
material intended for use in glass or ceramic manufacture. 


" Marketing Metals and Minerals." By J. E. Spurr and F. E. Wormser. New York, 1925, 674 pp. 

(Felspar, pp. 300-12.) 
" Feldspar." By O. Bowles and C. V. Lee. U.S. Bur. Mines, Inform. Circ. No. 6381, 1930, 21 pp., 

including bibliography. 
" Commercial Standards for Feldspar." U.S. Bur. Stand. Specif. C.S. 23-30, 1930. 
" Felspar." By H. S. Spence. Canad. Dept. Mines, Mines Br. Bull. 731, 1932, 145 pp. 
" Nepheline Syenite: A New Ceramic Material from Ontario." By H. S. Spence. Amer. Inst. 

Min. Met. Tech. Paper No. 951, Mining Tech., 1938, 9 pp. 
" Development and Growth of the Feldspar Industry." By H. B. Du Bois. Bull. Amer. Ceram. 

Soc, 1940, 19, 206-13. 
" Dental Feldspar, Typical Analysis." Anon. Foote-Prints, 1941, 14 (No. 2), 32. 
" Marketing Feldspar." By R. W. Metcalf. 17.5. Bur. Mines, Inform. Circ. No. 7184, 1941, 13 pp. 

including bibliography. 
" Ceramic Glazes." By F. Singer. Borax Consolidated Ltd., 1943, 95 pp. 
" Froth Flotation as Applied to Feldspar." By E. W. Koenig. Ceram. Age, 1946, 49, 47. 
"Non-metallic Minerals." By R. B. Ladoo and W. M. Myers. New York, 1951. (Felspar, pp. 

" Literature Abstracts of Ceramic Applications of Nepheline Syenite." By C. J. Koenig. Ohio 

State Univ. Eng. Exper. State Bull. 167, 1958, 63 pp. 
" Application of Electrostatics to Feldspar Beneficiation." By E. Northcott and I. M. Le Baron. 

Min. Eng., 1958, 10, 1087-1093. 
" Feldspar, Nepheline Syenite and Aplite." By J. E. Castle and J. L. Gillson. " Industrial 

Minerals and Rocks." Amer. Inst. Min. Met. and Petrol. Engnrs., New York, 1960, 3rd Ed. 

pp. 339-362. 
"Feldspar." By T. de Polo. " Mineral Facts and Problems." U.S. Bur. Mines Bull. 585, 1960, 

7 pp. 
" Feldspar, Nepheline Syenite and Aplite." Minerals Yearbook. U.S. Bur. Mines (Annual). 


Fluorspar and Cryolite 


Fluorspar, which is also known as fluorite or fluor, and in Great Britain as Derby- 
shire spar, consists essentially of calcium fluoride (CaF2). 

Fluorite is a rock-forming mineral found most abundantly in ore veins, particu- 
larly those carrying galena and zinc-blende in sedimentary formations. 

When pure, fluorite contains 51 1 per cent, of calcium and 48 19 per cent, of 
fluorine. It has a specific gravity of 3 • 1 8 and a hardness of about 4. 

It is of considerable importance as it is not only a valuable flux but also the only 
important commercial source of the element fluorine. 

Individual fluorspar crystals are not often seriously contaminated by included 
impurities, but the mineral frequently occurs associated with gangue minerals such 
as barytes, limestone, quartz, zinc-blende and galena, from which it must be 
separated to render it marketable. 

Separation processes may consist of crushing, hand picking, screening, jigging or 
other form of gravity concentration, flotation or decrepitation. Concentration by 
flotation or heavy media methods is becoming increasingly common in the U.S.A. 
and decrepitation methods have been employed in British Columbia and New 
•Mexico. Froth flotation is used to produce a high-grade product of fine particle size; 
sink-float methods give a coarse size product such as is required for metallurgical 

World Production 

During World War II the total production of fluorspar was more than doubled 
as compared with an output in 1938 of about 400,000 long tons, and reached a peak 
of about 950,000 long tons in 1943, excluding the production of the U.S.S.R. 

The world's recorded production of fluorspar in 1958 totalled about 1,500,000 
long tons, excluding the outputs from Belgium, Brazil and N. Korea. The countries 
with the largest production were, Mexico, United States, the U.S.S.R., China, Italy, 
Federal Germany, United Kingdom, France, Spain, Eastern Germany, Canada 
and the Union of South Africa. Great Britain produced 77,505 long tons of 
fluorspar in 1958. The largest importers of fluorspar are the United States, the 
U.S.S.R., Japan and Canada. 


The principal uses for fluorspar, roughly in order of importance, are (1) as a flux 
in the production of basic open-hearth steel and in other metallurgical operations 
such as the smelting of copper and lead ores; (2) for the production of hydrofluoric 
acid, elemental fluorine and fluorides; (3) as a flux and opacifier in glassmaking. 
Fluorspar is also used in the electrolytic refining of lead and antimony and in the 
manufacture of artificial cryolite for use in the reduction of alumina to metallic 

h2 195 


No official statistics are available to show the consumption of fluorspar by the 
various industries in Great Britain, but those for the United States are given in 
Table 69. 

Table 69 

Fluorspar consumed by Industries in the U.S.A.* (In short tons) 







Basic Open Hearth Steel 






Electric Furnace Steel 






Bessemer Steel . 






Iron Foundry . 






Ferro Alloys 






Hydrofluoric Acidf 






Primary Aluminium 




"V 2,529 


Primary Magnesium . 




Glass .... 






Enamel .... 






Cement .... 






Miscellaneous . 






Total .... 






* From " Minerals Yearbook," U.S. Bur. Mines. 

t Fluorspar used for making artificial cryolite and aluminium fluoride is included in the 
figures for hydrofluoric acid, an intermediate in their manufacture. 

t Including welding rod coatings, 2,316; special flux, 7,959; and non-ferrous uses, 5,372. 

** 1 174 2S7 7 137 

Metallurgical Uses. Between 70 and 80 per cent, of the world's production of 
fluorspar is used in the basic open-hearth process of steel-making, the mineral being 
added at the rate of 5-8 lb. per ton of steel produced. 

The consumption of fluorspar for steel manufacture in the United States has 
been considerably reduced during the past decade, as is shown by the following 
figures which give lbs of fluorspar consumed per short ton of steel produced. 

1948-52 1954 1955 1956 1957 1958 


Basic open hearth . . 5-3 4-4 4-3 4-8 4-2 40 

Electric furnace . . .9-6 7-9 8-9 8-2 6-4 7-4 

Other metallurgical uses are in the production of certain ferro alloys, in electric 
steel-smelting, smelting and refining of lead, antimony and silver ores, and in 
foundry work. When used in electric steel-smelting the consumption of fluorspar 
may vary from 14 to 40 lb. per ton of steel produced, according to the quality of 
fluorspar used. The annual consumption of fluorspar in Great Britain for metal- 
lurgical purposes amounts to about 64,000 long tons. 

The grade of fluorspar used for fluxing, often termed " gravel," is usually sized 
from \ or £ in. to dust, but the percentage of fine or " sand " grade should be small. 
Occasionally, however, larger-sized material is specified, as at one large works in 
the Union of South Africa which requires the fluorspar in lumps 1-4 in. in diameter. 



It usually carries about 85 per cent, calcium fluoride (CaF2), with not more than 6 
per cent, silica and 0-3 per cent, sulphur. During World War II, however, sales were 
made in the United States on the basis of 78 per cent. CaF2 (with a minimum of 
55 effective units) and sulphur not exceeding 1 per cent. 

Effective units are calculated by deducting from the percentage of calcium 
fluoride about twice the percentage of silica present. The presence of silica is objec- 
tionable when the mineral is used as a flux, as 6 per cent, will neutralize about 15 
per cent. CaF2. Barytes is objectionable as it decreases the fluidity of the melt. 
Other undesirable impurities, if present in quantity, include lead and zinc sulphides, 
phosphates and metallic sulphates. 

Iron foundries often employ a large-sized product ranging up to 5 or 6 in. in 

The U.S. National Stockpile Specification P-69b, dated July 24th, 1951, for the 
purchase of metallurgical grade fluorspar, provides for two grades as shown in 
Table 70. 

Table 70 

Metallurgical Grade Fluorspar: U.S. National Stockpile Specification P-69b 

Grade A 

Grade B 

Effective calcium fluoride, CaF 2 , min.* . 

Sulphur (present as sulphide and/or free sulphur), 

S, max 

Lead, Pb, max 

Per cent. 


Per cent. 


* Effective CaF 2 is calculated by deducting 2 per cent, from the contained CaF 2 
for each 1 per cent, of silica present. 

All material must pass a 1 in. opening and not over 15 per cent, may pass a No. 
16 U.S. Standard screen. 

Chemical Uses. Fluorspar provides the only large-scale commercial mineral 
source of fluorine and hence is used in the production of hydrofluoric acid and the 
fluorides, the demand for which is increasing, particularly for the production of the 
Freon types of refrigerants. Certain inorganic fluorides also find a wide use as 
insecticides, antiseptics and for etching glass. The grade used, frequently termed 
" acid spar," should contain about 95-98-5 per cent. CaF2, while impurities should 
not exceed the following percentages: silica 1 -5; calcium carbonate 1-1 -25; sulphur 

High grade ground fluorspar, as marketed by the Glebe Mines Ltd., of Eyam 
near Sheffield, England, has the composition shown in Table 71. 

Chemical manufacturers usually require material ground to pass a 100-mesh 
sieve and this provides an outlet for the high-grade material produced by flotation 
concentration, which would be too small for use in steel-making. 

The U.S. National Stockpile Specification P-69a, dated February 13th, 1952, for 
the purchase of acid grade fluorspar, provides for two grades: (1) hydrofluoric acid 



Table 71 

High Grade Ground Fluorspar. 

Eyam, England. 

Per cent. 

Chemical Analysis: 

Calcium fluoride, CaF2, min. 

Silica, Si02, max. 

Barium sulphate, BaS04, max. . 

Calcium carbonate, CaCOs, max. 

Sulphides, max. 

Iron and Aluminium oxides, FeuOa, AI2O3, max. 
Approximate cumulative screen analysis: 

All passing 60-mesh 

+ 100-mesh 

+ 150-mesh 

+ 200-mesh 

- 200-mesh 

98 00 


grade; (2) cryolite grade suitable for the manufacture of synthetic cryolite. The 
chemical composition specified for the two grades is shown in Table 72. 

Table 72 
Acid Grade Fluorspar: U.S. National Stockpile Specification P-69a 

Acid Grade * 

Grade * 

Calcium fluoride, CaF 2 , min 

Silica, Si0 8 , max 

Sulphur (present as sulphide and/or free sulphur), 

S, max 

Calcium carbonate, CaCOj, max 

Iron oxide, Fej0 3 , max. ..... 

Lead, Pb, max 

Zinc, Zn, max 

Per cent. 

97 1 



Per cent. 
97 t 



* Dry basis. 

t CaF a may be 95 per cent, (min.) provided that the available CaF a is not less 
than 91 per cent. Available CaF 2 is calculated by deducting 4 per cent, from the 
total for each 1 per cent. SiO s . 

t May be 95 per cent, (min.) provided that the CaCO a is 1 00 (min.) and that the 
CaCO, shall not be less than 1-5 per cent, for each 1 per cent, that the CaF s is 
below 97 per cent. 

Fluorine compounds are being increasingly used for addition to drinking water, 
to reduce the incidence of dental caries, the amount added being equivalent to about 
1-1 -5 parts of fluorine per million. In the United States the addition was officially 
accepted by the American Waterworks Association in 1949, and about 70 per cent, 
of the States have accepted the recommendation. It is stated, however, that about 
eight years must elapse before the beneficial results will be confirmed definitely. 



It was estimated that more than 34 million people, distributed through 1,650 
cities and towns in the United States were drinking fluorinated water at the end 
of 1958. In Great Britain the treatment of drinking water supplies with fluorine 
compounds has been in operation for about three years, under the auspices of the 
Ministry of Health, in three demonstration areas, i.e. Anglesey, Kilmarnock and 
Watford. If beneficial results are obtained in these areas, it seems probable that 
the treatment will be adopted in other districts. 

Elemental fluorine is a very highly reactive light yellow gas which can be con- 
densed to a yellow liquid which boils at — 187°C. and freezes to a yellow solid at 
about — 233° C. It is prepared on an industrial scale by the electrolysis of a mixture 
of highly purified anhydrous hydrogen fluoride and potassium fluoride at about 
105-1 10° C. The fluorine is evolved in the anode compartment and contains about 
10 per cent, of hydrogen fluoride which is removed later by absorption by sodium 
fluoride. Fluorine can be stored in nickel cylinders at about 450 lb. per sq. in. pressure 
and is now marketed in this form in Great Britain by the Imperial Smelting Corpora- 
tion Ltd. 

Elemental fluorine is extremely reactive and difficult to handle and for many 
purposes it can be replaced by chlorine trifluoride, which is a stable liquid having 
three highly reactive fluorine atoms. Other fluorine compounds produced com- 
mercially in Great Britain include boron trifluoride, fluosulphonic acid and 
benzo-trifluoride, the latter being of use as a dyestuff intermediary. 

Before World War II, the preparation of gaseous fluorine was only carried out 
on an experimental scale and with some difficulty. In 1942, however, a demand arose 
for fluorine on a fairly large scale in connection with the production of the atomic 
bomb. It had been found that the most convenient method then known for the 
separation of uranium-235 from the other isotopes was by a gaseous diffusion 
process using uranium hexafluoride (UF 6 ) and this necessitated the use of gaseous 
fluorine on a large scale. Also, as UF 6 is one of the most highly reactive substances 
known, much research had to be carried out on the best type of plant to be used in 
the preparation and fractionation of the gas. Amongst the substances studied were 
the " fluocarbons " — compounds containing only carbon and fluorine and made by 
substituting fluorine for hydrogen in certain hydrocarbons derived from petroleum. 
The fluocarbons, which vary in properties from non-inflammable gases to waxy 
solids, are characterized by their resistance to heat, chemical action, acids, alkalis, 
and fluorine. 

Although the fluocarbons are no longer required for use in handling uranium 
hexafluoride, some of them have industrial importance. 

Since 1946 considerable progress has been made in the commercial production 
of certain fluocarbon plastics, such as " Fluon " (by Imperial Chemical Industries 
Ltd.), "Teflon" (by E. I. Du-Pont de Nemours & Co.), "Kel-F" (by M. W. 
Kellogg & Co.), " Fluorothene " (by Bakelite Ltd.) and " Exon 400 x R— 61 " 
(Firestone Tyre and Rubber Co. Ltd.). " Fluon " and " Teflon " are high polymers 
of tetrafluoethylene, having remarkable resistance to many solvents and corrosive 
chemicals. In general, however, polytetrafluoethylenes are difficult to fabricate by 
the processes used for most plastics: they are used for making packing, insulating 



tape, and for lining reaction vessels made of steel, copper, aluminium, glass or 
ceramics. Chlorotrifluoroethylene polymers developed by M. W. Kellogg & Co., 
the Carbide and Chemical Corporation Ltd. and E. I. Du-Pont de Nemours, are 
stated to be rather more easily moulded than the above mentioned polytetrafluo- 
ethylenes. " Exon 400 x R — 61 " is stated to be a copolymer of vinylidene fluoride 
and chlorotrifluoroethylene which can be injection-moulded at 435° F. and 10,000 
lb. p.s.i. pressure. It can be heated in air to 350° F. for 100-200 hours without 
detriment to its physical properties. " Fluorothene," a monochlorotrifluoro- 
ethylene polymer is stated to be capable of withstanding temperatures up to 480° F. 
for long periods, to have good electrical properties, dimensional stability and low 
temperature characteristics. It is supplied in powder form, which can be either 
injection or compression moulded. 

Fluorocarbons are manufactured by reacting anhydrous hydrofluoric acid with a 
chlorinated hydrocarbon under the catalytic influence of such inorganic fluorides 
as antimony fluoride or chromium fluoride. They are being manufactured in Great 
Britain by Imperial Chemical Industries Ltd. and the Imperial Smelting Corporation. 

Imperial Chemical Industries Ltd. also produce anhydrous hydrogen fluoride, 
difluorodichloromethane (" Arcton 6 "), difluoromonochloromethane (" Arcton 
4 "), monofluorotrichloromethane (" Arcton 9 ") and polytetrafluoroethylene. The 
Arcton products are used as refrigerants and are comparable with the " Freons " 
which have been extensively used in the United States for the same purposes. These 
refrigerants, which have the advantage of being non-toxic and non-inflammable, 
can also be used as intermediaries for the manufacture of other fluorine compounds. 

Anhydrous hydrofluoric acid is also produced by a continuous process by the 
Imperial Smelting Corporation at Avonmouth. The fluorspar used, which all passes 
a 120-mesh screen, and 75 per cent, through 200-mesh, is required to contain not less 
than 97 per cent, of CaF2, less than 1 per cent, each of silica and calcium carbonate 
and under 0-1 per cent, of sulphide sulphur. The consumption of fluorspar in Great 
Britain for the manufacture of hydrofluoric acid amounts to about 10,000 long tons 
per annum. 

Fluorinated ethanes, under the name of " Genetrons," are made in the United 
States and used in the " Aerosol " fumigator or " bug bomb " which is used for 
exterminating mosquitos, flies and other disease-carrying insects in enclosed spaces. 

Fluorosilicic acid is used as a disinfectant for copper and brass vessels used in 
brewing. Sodium silico-fluoride finds use as a laundry scourer, as a flux in metallurgy 
and as an opacifier in ceramics. The annual consumption of this compound in the 
United States amounts to over 10,000 tons. 

Electroplating. British Standard Specification No. 2657 : 1956 covers fluoboric 
acid and metallic fluoborates for electroplating. 

As regards fluoboric acid two grades are specified, Grade 1 for general electro- 
plating purposes and Grade 2 for the preparation of lead fluoborate solution in the 
electrodeposition of lead and in the preparation and maintenance of baths of 
copper fluoborate for the electrodeposition of copper. 

The material shall be a clear, colourless or nearly colourless, aqueous solution of 
fluoboric acid containing not less than 40 per cent, by weight of fluoboric acid 



calculated as HBF4. The material shall contain not less than one per cent, and not 
more than 5 per cent, by weight of free boric acid calculated as H3BO3, when 
determined by the prescribed method. The impurities present in fluoboric acid shall 
not exceed the following percentage limits : 

Grade 1 

Grade 2 

Per cent. 

Per cent. 

Sulphates, calculated as SO4 



Silica „ „ Si0 2 



Iron „ „ Fe 



Heavy metals, other than iron 



Chloride, calculated as CI . 



The Specification requires that lead fluoborate for electroplating shall be a clear, 
colourless or nearly colourless, aqueous solution of lead fluoborate approximating 
to the formula Pb(BF4>2. The material shall contain not less than 28 per cent, by 
weight of lead, calculated as the metal, and the impurities present must not exceed 
the following percentage limits: silica, calculated as Si02, 1-0; iron, calculated as 
Fe, 01. The amount of free acid, calculated as HBF4, shall not exceed 2 per cent, 
by weight, when determined by the prescribed method. The amount of free boric 
acid, calculated as H3BO3 shall be not less than 0-6 per cent, by weight and not more 
than 3 -0 per cent, by weight when determined by the prescribed method. 

The Specification also requires that tin fluoborate for electroplating shall be a 
clear, colourless, or nearly colourless, aqueous solution of stannous fluoborate, of 
formula Sn(BF4)2, and shall contain not less than 19 per cent, by weight of tin in the 
stannous form, calculated as metal. The impurities present shall not exceed the 
following percentage limits: sulphate, calculated as SO4, 0-4; silica, calculated as 
SiOz, 0-1; iron, calculated as Fe, 1; chloride, calculated as CI, 01; copper, 
calculated as Cu, 0-005. The amount of free acid in the solution of tin fluoborate, 
calculated as HBF4 shall not exceed 10 per cent, by weight, when determined by 
the prescribed method. The amount of free boric acid, calculated as H3BO3 shall 
be not less than 1 -0 per cent, and not more than 5 -0 per cent, by weight, when 
determined by the prescribed method. 

The Specification requires that copper fluoborate for electroplating shall be a 
clear, blue, aqueous solution of cupric fluoborate, formula Cu (BF4)2, containing not 
less than 12-5 per cent, by weight of copper, calculated as metal. The amount of 
impurities present shall not exceed the following percentage limits : silica, calculated 
as S1O2, 10; sulphate, calculated as SO4, 2-5; iron, calculated as Fe, 0-2. The 
amount of free acid in the solution of copper fluoborate calculated as HBF4 shall 
not exceed 2 per cent, by weight when determined by the prescribed method. The 
amount of free boric acid calculated as H3BO3 shall be not less than 0-75 per cent, 
by weight, and not more than 3-75 per cent, by weight when determined by the 
prescribed method. 



Ceramic Uses. Fluorspar is used as a constituent of opalescent coloured and 
opaque glass. For this purpose the content of iron oxide should be fairly low — usually 
006-012 per cent. ; silica, which acts in this case chiefly as a diluent may be as high 
as 13 per cent, but usually material containing from 2-5 to 3 per cent, is preferred. 
Calcite and barytes should be less than 1 per cent, and compounds of lead and zinc 
should usually be absent. The consumption of fluorspar varies between 75 and 
500 lb. per 1,000 lb. of silica in the glass batch. Users often buy the material ready 
ground to pass a 100- or even 200-mesh sieve, but some require 40-mesh material. 
The best grade ceramic fluorspar contains 95-98 per cent. CaF2, with SiC>2, 2-3, and 
CaCOs, 1 per cent, or less. 

Fluorspar is also used as a flux and auxiliary opacifier in opaque, white and 
coloured enamels for coating metalware; the standards of purity adopted are 
similar to those mentioned above for glassmaking. It is essential that the percentages 
of iron, zinc and sulphur should be low, as these cause staining. 

Miscellaneous Uses. Fluorspar of a quality suitable for optical purposes is 
comparatively rare, the world's output being possibly not more than 1 ton per 
annum. For this purpose the fluorspar should be clear and free from cloudiness, 
inclusions, cracks or incipient cleavage marks. Colourless crystals are most desired, 
but occasionally material faintly coloured yellow or green may be used. It should be 
of such size as to permit clear plates of £-2 in. diameter being cut. The chief optical 
use for fluorspar is the construction of apochromatic lenses. 

Fluorspar has been suggested as an addition to the mixture used for making 
Portland cement, and it is stated that 3-5 per cent, may be advantageously added to 
reduce the sintering temperature of the mix. No specification is available for this 
use, but it seems unlikely that a high-grade fluorspar would be required, as low- 
grade fluorspar has been used in Germany for this purpose. 

Potassium fluotitanate is an important ingredient in the production of aluminium 
titanium alloys, for which purpose it can be used much more readily than the metal 
titanium, and sodium fluotitanate is now used as a coagulating agent for natural 
rubber latex. 

Sodium and potassium fluoborates are used in the light metal industry for grain 
refining, removal of oxide inclusions, etc. 

Fluosilicates of sodium, potassium or barium are used as insecticides for protect- 
ing field crops. Cryolite and synthetic sodium fluoaluminate are also used to some 
extent as insecticides, particularly against the codling moth in apples. Sodium 
fluoride is used in the United States as a household insecticide against ants and 
roaches, frequently in conjunction with pyrethrum dust, borax and alumina. 


Cryolite is a double fluoride of aluminium and sodium having the formula 
3NaF.AlFg and containing when pure 12-9 per cent, aluminium, 32-8 per cent. 
sodium and 54-3 per cent, fluorine. It may be found associated with the minerals 
fluorite, quartz, chalcopyrite, pyrite, siderite and galena. 

The mineral is not of common occurrence, in fact the only deposits workable on 



a commercial scale are at Ivigtut, in Greenland. Before World War II the greater 
part of the output was exported to selling agents in Pennsylvania, U.S.A. 

The exports of cryolite from Greenland have varied between 71,959 long tons in 
1952 and 40,323 long tons in 1958. 

Cryolite is chiefly used as a flux in the reduction of alumina to the metallic state. 
It is also used in the manufacture of enamels and opaque glass and in insecticides. 

Three grades of natural cryolite are marketed, the best containing a minimum of 
98 per cent, of sodium aluminium fluoride with maxima of 1 -5 per cent, silica; 0-25 
per cent, iron oxide, and lime usually under 1 per cent. The other two grades carry 
93-94 per cent, of cryolite with iron oxide not exceeding 0-75 per cent. 

Artificial cryolite is made in several European countries, Canada, and in the 
United States. The usual method of manufacture is by causing aluminium fluoride to 
react with hydrofluoric acid and a sodium salt. In another process, sodium fluoride 
and aluminium hydrate are digested together at approximately 175° C. In a German 
process, ammonium fluoride is made to react with an aqueous sodium aluminate, 
Na 3 A10 3 , solution obtained in the manufacture of alumina. Siliceous fluorspar is 
used for the preparation of the ammonium fluoride. 

Artificial cryolite is sometimes used as a substitute for fluorspar in the ceramic 
industry, the amount being usually 3-5 per cent, of the enamel batch: occasionally, 
however, up to 12 per cent, may be used. 


" Fluorspar; Its Mining, Milling and Utilization." By R. B. Ladoo. U.S. Bur. Mines, Bull. No. 

244,1927, 185 pp. 
" Iceland Spar and Optical Fluorite." By H. H. Hughes. U.S. Bur. Mines, Inform. Ore. No. 

6468, 1931, 17 pp., including bibliography. 
" Fluorspar as a Chemical Raw Material." By F. H. Reed and G. G. Finger. Chem. Indus. 

(N.Y.), 1936, 39, 577-81. 
" Cryolite from Fluorspar." By F. C. Frary. Steel, 1941, 108 (June 30), 4 pp. 
" Fluorspar: Raw Material for the Process Industries." By H. G. Hymer. Chem. Met. Engng., 

1945, 52 (August), 98-9, 111 and 134. 
" Fluorine: Preparation, Production and Handling." A symposium by various authors. Industr. 

Engng. Chem., 1947, 39, 244-80. 
" Cryolite as an Insecticide." By J. G. Brunton. Agric. Chemicals, 1947, 2 (No. 8), 26-8 and 64. 
" Present and Future Trends in the Use of Fluorspar and Fluorine Compounds." By A. J. P. 

Wilson. Chem. Engng., 1948, 55, 313-4. 
" Chemistry and Use of Insecticides." By E. R. de Ong. New York, 1948. (Sodium fluoride and 

fluosilicates, pp. 100-02.) 
" Fluorine Progress." By R. W. Porter. Chem. Engng., 1948, 55, 102-05. 
" The Preparation, Properties and Handling of Elemental Fluorine." By A. J. Rudge. Chem. and 

Ind., 1948, p. 731. 
" The New Fluocarbon Chemistry." By M. Stacey. Royal Institute of Chemistry, 1948, 15 pp. 
*' The Production of Anhydrous Hydrofluoric Acid." Anon. Industr. Chem., 1948, 24, 801-11. 
" Polytetrafluoroethylene: Its Development and Methods of Fabrication." (" Fluon " and 

" Teflon "). By J. W. Fergusson. Chem. and Ind., 1949 (Aug. 20th) 586-90, including biblio- 
" Fluorspar and Cryolite." By H. T. Mudd. Industrial Minerals and Rocks, 2nd Ed. Amer. Inst. 

Min. Eng., New York, 1949, pp. 381^*03. 
" The Production of Cryolite by the Fluoboric Process." By H. W. Heiser. Chem. Engng. Prog., 

1949, 45, 167-79. , , „ . , , 

" Fluorspar and Fluorine Chemicals." Pt. 1. " Economic Aspects of the Fluorine Industry. By 

N. T. Hamrich and W. H. Voskill, 46 pp. 
" Fluorine Chemicals in Industry." By G. G. Finger and F. H. Reed. State Geol. Surv., Illinois, Rep. 

Invest. No. 141, 1949, 46 pp. 
"Non-metallic Minerals." By R. B. Ladoo and W. M. Myers. New York, 1951. (Fluorspar, 

pp. 220-32, including bibliography.) 
" Preparation, Properties and Technology of Fluorine and Organic Fluoro Compounds." By 

S. Slesser and S. Schram. New York, 1951, 868 pp. (National Nuclear Energy Series.) 



" Plastics Progress." 1953, British Plastics Convention, 1953. 

" Phosphate Rock as an Economic Source of Fluorine." By W. L. Hill and K. D. Jacobs Min 

Eng., 1954, 6 (Oct.), 994-1000. 
" Fluorine." By L. Domange. " Nouveau Traite de Chimie Minerale." Ed. by P. Pascal. Paris, 

I960, xvi, 17-149. 
" Fluorspar and Cryolite." By R. M. Grogan. "Industrial Minerals and Rocks." Amer. Inst. Min. 

Met. Petrol. Engnrs., 3rd Ed., 1960, 363-382. 
" Fluorspar and Cryolite." Minerals Yearbook. U.S. Bur. Mines (Annual). 
" Fluorine." By R. B. McDougal. " Mineral Facts and Problems." U.S. Bur. Mines Bull. 585, 

1960, 11 pp. 


British Standards Institution: 

Fluoboric Acid and Metallic Fluoborates for Electroplating. B.S. 2657 : 1956. 
U.S. National Stockpile Specifications: 

Acid Grade Fluorspar. P-69a, Feb. 13th, 1952. 

Metallurgical Grade Fluorspar, P-69b, July 24th, 1951. 

Fullers' Earth 

The name fullers' earth is applied to certain non-plastic, or semi-plastic, soft clay- 
like minerals which are characterized by the fact that they adsorb grease and remove 
colouring matters from oils and some basic dyes from other liquids, including water. 
Many clays show these characteristics, but only those which show them to a very 
marked degree should be classified as fullers' earth. 

Fullers' earths, like most clay minerals, consist essentially of hydrated silicates 
of aluminium with variable amounts of iron oxide, magnesia, lime, and alkalis. 
Their industrial value, however, depends less upon their chemical analyses than on 
the physical properties which follow from their structure. Fullers' earths are calcium 
montmorillonites; but in the United States all montmorillonites are called benton- 
ites, with the prefixes " swelling " and " non-swelling " for the sodium and calcium 
members, respectively, of the group. Attapulgite, a distinct clay mineral, is termed 
fullers' earth. Most fullers' earths are slightly alkaline, partly owing to some of the 
mineral impurities and partly because the sodium and calcium montmorillonites 
act as salts of weak acids and strong bases. Clays containing hydrogen montmoril- 
lonite, which confers an acid reaction, are known. 


In Great Britain fullers' earth is obtained by open-cast working or drift mining. 
After World War I, the demand for fullers' earth fell considerably owing to the 
production in Germany of acid activated clay, which was superior to English fullers' 
earth or American " Floridin." Later, however, methods were devized both in 
Great Britain and the United States for activating fullers' earth. British activated 
fullers' earth is used by all large oil refineries in this country and is also exported. 

The treatment which the crude earth, as quarried, has to undergo to render it 
suitable for industrial uses varies considerably. Some earths may be used almost 



without treatment, except careful drying to remove surplus hygroscopic moisture. 
If artificial heat is used, care has to be taken to avoid overheating and so expelling 
the combined water and decreasing the efficiency of the earth. The dried material is 
then ground to a powder or is prepared in granulated form by crushing and sieving 
to various grain sizes to suit individual user's requirements. 

In the U.S.A. attapulgite is treated as follows: after air-drying for several weeks 
the earth is crushed to approximately |-in. size and then dried to about 16 per cent, 
moisture in horizontal rotary driers. The earth is then further crushed by passing 
through corrugated rolls, after which it is sieved to the required grain size. A 
product obtained from attapulgus by the Minerals and Chemical Corporation 
of America is marketed under the name of " Attacote " as a coating for use on 
hygroscopic or sticky chemicals to prevent caking. It consists of needle-like, cream- 
coloured particles of 8 microns average size, having a specific gravity 2-047, bulk 
density of 16 lb. per cu. ft., oil absorption of 79-8, and it leaves only 1 -5 per cent, 
on a 325-mesh sieve. It has a surface area of 125 sq. in./gm. It is stated to have been 
used for several years for coating ammonium nitrate and ammonium sulphate, the 
quantities used varying between 0-5 and 2 per cent, of the product treated. A 
specially fine product called " Attasorb LVM " is made for use in the conditioning 
or anti-cracking agent for phenolic resins. 

Natural fullers' earth produced and marketed in Great Britain may contain 
calcite (CaCOs) in amounts varying from mere traces up to 30 per cent. Felspar is 
nearly always present in small quantities, together with apatite, barytes, zinc- 
blende and pyrite. The weathered yellow grades of earth usually contain a little 

The chemical composition of some fullers' earths from various localities is 
shown in Table 73. 

Table 73 

Composition of Non-activated Fullers' Earth. 
Per cent. 

Calcium Montmorillonite 


Nuffield Surrey 





S. Dakota 






Silica, Si0 2 








Alumina, AJ2O3 








Ferric oxide, FeaOa . 








Lime, CaO 








Magnesia, MgO 








Soda, Na 2 . 








Potash, K2O . 








Carbon dioxide, CO2 ■ 








Loss on ignition, 

(excluding CO2)* . 








* Miscellaneous items such as moisture, Ti02, BaO, P2O5 and F included in loss on 



The preparation of acid activated fullers' earth is usually carried out by heating 
the clay with sulphuric or hydrochloric acid solutions for a prolonged period, fol- 
lowed by washing to remove the surplus acid and soluble salts produced during the 
activation process. Finally the clay is dried carefully and ground. 

World Production 

The world's more important producers of fullers' earth include the United States, 
Great Britain, Germany, France, Hungary, Canada, Algeria, Japan and India. 
The world's annual production is probably nearly one million tons, but statistics are 
very incomplete. Of the countries which recorded production of fullers' earth in 
1958, the United States reported 319,538 long tons (sales), India 13,483 long tons, 
Union of South Africa 1,759 long tons, Australia 120 long tons. 


At one time the mineral was principally used by fullers, who employed it as a 
detergent to remove greasy matter from woollen goods, and also in felting and the 
shrinking processes, known as fulling, and applied to woollen cloth. Although these 
processes still persist to some extent, the chief present-day use for both the natural 
and activated products is for removing coloured or otherwise undesirable natural 
ingredients from animal, vegetable and mineral oils. Fullers' earth is finding 
increasing use as a filler, or dusting powder, and is also employed in cosmetics, and 
as a base for adsorbing green dyes. Its use as a cheap, solid catalyst for esterification, 
hydrolysis, alkylation, polymerization and cracking has recently received consider- 
able attention. 

Many of the uses of fullers' earth depend for their efficiency on the colloidal 
properties of the montmorillonite constituent, which can adsorb much moisture, 
but does not ball and can still be blown into dust. Hence, fullers' earth is a good base 
for the preparation of non-silicotic mine-dusting powders and as a carrier for 

Table 74 
Fullers' Earth: Consumption by Uses in the United States* 


Percentage of total 







Absorbent uses 
Mineral oil refining 
Insecticides and fungicides 
Rotary drilling muds 
Vegetable oil refining . 
Other uses .... 















Total tonnage sold or used by 
producers (short tons) 







♦From " Minerals Yearbook," U.S. Bur. Mines. 



Dried fullers' earth (especially the sodium type) has a specific gravity varying 
between 2-55 and 2-68, disperses freely in water and forms thixotropic gels. Both 
calcium and sodium montmorillonite have the property of adsorbing many colour- 
ing matters and of acting as a bond. 

A number of grades of English fullers' earth, specially adapted for particular uses 
are produced and marketed by The Fullers' Earth Union Limited, who also prepare 
activated earths for treating mineral and glyceride oils. 

The consumption of fullers' earth in the United States by industries is shown in 
Table 74. 

Bleaching Oils. Generally, it is more economical to use an activated form of 
fullers' earth for this purpose. The activity, which is produced by acid treatment, 
may be as much as three to seven times that of the natural earth. In some cases 
activated earths will bleach oils which are practically untouched by natural earth. 
About thirty years ago activation was started in this country and during World 
War II the whole requirements for refining every type of oil were supplied from 
British material. The desirable characteristics of fullers' earth intended for bleaching 
edible oils are : (1) the oil should be thoroughly bleached by the earth and should not 
revert to its original colour on standing; (2) the oil should filter easily; (3) no odour 
should be imparted to the refined oil by the earth; (4) the quantity of oil retained by 
the cake should be small; (5) no spontaneous ignition should occur either in the 
filter press or in the waste pits. As a general rule it is not possible to revivify fullers' 
earth which has been used for treating oils. 

In bleaching edible oils, the neutralized oil is treated with a small percentage of 
activated earth at a temperature of about 85° C. for an hour with constant stirring. 
The oil is removed from the spent earth in a filter press and is then ready to be re- 
deodorized. A similar process is used as a step in refining lubricating oils and is 
known as the contact process ; it is suitable for oils which are specially light coloured. 
It is more usual, however, to treat lubricating oils by the steam stripping process, in 
which a mixture of the earth and the oil is heated, in the absence of air, to a temper- 
ature which may be as high as 275° C, while at the same time super-heated steam is 
blown through it. 

Some lubricating oils are refined with granular earth which may be either 
attapulgite or a specially manufactured product. The granules, usually about 30- 
mesh, are placed in a tower and the oil is passed through at a suitable temperature 
until the decolorizing power of the earth is exhausted. 

Some of the new processes for the catalytic cracking, polymerization and re- 
forming of petroleum to produce high-grade petrol also employ powdered or granu- 
lar activated fullers' earth as catalyst. In each of these cases it is possible to regener- 
ate the catalyst. It has been suggested that the waste product, when no longer 
suitable for oil refining, might be used to replace, in part, the sand in gypsum 
plasters, or, after ignition, as a decolorizer in the purification of industrial water 
supplies. Other suggested uses include employment as a filler in bitumen on account 
of the very large surface area of the earth; as a carrier or diluent for insecticides and 
as a waterproofing agent in concrete. 

In general, the only satisfactory method of ascertaining whether the fullers' earth 



from any particular locality is suitable for oil refining, is to carry out practical trials 
with the oil in question under conditions of use. Promising materials should have 
a cation exchange capacity between 50-100 m.e./lOO gm. and X-ray analysis should 
indicate a high concentration of montmorillonite or attapulgite. 

Other Uses. Owing to its adsorptive properties, soft texture and freedom from 
grit, fullers' earth finds use in cosmetics, industrial protective creams and foot 
powders. It is also used in several manufacturing processes on account of its 
adsorptive capacity for vitamins and alkaloids. 

A montmorillonite product made by the Fullers' Earth Union is claimed to be 
suitable for use as an absorbent in a process for the disposal of long-lived fission 
products from the atomic pile, such as Sr-90 and Cs-137. In its natural state 
montmorillonite clay disperses in water to form a mud, which at high activity levels 
would be difficult to handle. This difficulty is overcome by bonding the clay with 
hydrolyzed ethyl silicate to form water-soluble granules. The solution containing 
the fission products is circulated over the granules until the latter are saturated. The 
fission products are then fixed on the granules by firing the latter to 1,200°C. or 
higher. The fired material is then sent in canisters to long-term underground storage 

Fullers' Earth Derivatives 

In addition to the natural and activated fullers' earth referred to above, several 
products of industrial importance were developed in Great Britain by The Fullers' 
Earth Union Limited, during World War II. They include products originally 
marketed under the name of " Union Bentonite," later known as " Fulbent," and, 
in an improved form, as " Fulloid." " Fulloid " can replace American bentonite in 
making oil-well drilling muds, and " Fulbents " used as suspending agents in 
aqueous media, and as bonding agents in the manufacture of refractory products. 

A new type of fullers' earth product has recently been developed by The Fullers' 
Earth Union Limited under the name of E. M. Granules. This is usually available 
in the form of 10-30-mesh granules which do not break down in aqueous solutions 
or organic solvents and can be used for cation exchange in column operations. The 
c.e.c. is about 45-50 m.e. per 100 ml. granule bed. One suggested use is for the 
removal of radioactive cations from the waste effluent of atomic power stations. 

Another series of products known as " Fulbonds " are widely used in the foundry 
industry. Grades are prepared for use in the ferrous, non-ferrous and light alloy 


" Fullers' Earth and its Application to the Bleaching of Oils." By C. L. Parsons. /. Amer. Chem. 

Soc, 1907, 29, 598. 
" Fullers* Earth." By C. L. Parsons. U.S. Bur. Mines, Bull. No. 71, 1913, 38 pp. 
Fullers' Earth and its Value for the Oil Industry." By T. G. Richert. Ind. Eng. Chem., 1917, 9, 

jyy — ouo. 
" Fullers' Earth." Anon. Imp. Min. Res. Bur., Lond., 1920, 15 pp. 

Fullers' Earth." Anon. Bull. Imp. Inst., 1924, 22, 460-71. 
" Marketing Metals and Minerals." By J. E. Spurr and F. E. Wormser. New York, 1925, 674 no 

(Fullers' Earth, pp. 326-32.) 
" cla y s: Jheir Occurrence, Properties and Uses." By H. Ries. 3rd Ed., Lond., 1927. (Fullers' 

Earth, pp. 375-85.) 



" The Bleaching Earths." By P. G. Nutting. Ind. Eng. Chem. (Anal.), 1932, 4, 139-41. 

" Industrial Utilisation of Decolorising Clays." By L. Delemon. Chim. et Industr., 1934, 31, 432. 

" Bleaching Clays Find Increasing Uses." By G. A. Schroter. Eng. Min. /., 1939, 140 (Nov.), 

35-8 and 40 (including bibliography). 
" Modern Concepts of Clay Materials." By R. E. Grim. /. of Geo!., 1942, 50, 225. 
" Adsorbent Clays." By P. G. Nutting. U.S. Geol. Surv., Bull. No. 928C, 1943, 94 pp. 
" Adsorbent Earths Industry." By A. Ackermann. Chim. et Industr., 1944, 51, 29-37. 
" Application of the Theory of Oil Bleaching." By J. L. Boyle. Manuf. Chem., 1946, 17, 97-8. 
" Clay Research and Oil Development Problems." By J. G. Griffiths. /. Inst. Pet., 1946, 32, 18-31 

(including bibliography). 
" Use of Fullers' Earth in Foundries." By L. V. Roy. Found. Tr. J., 1948, 84, 271-4. 
" Fullers' Earth : Some Notes on its Mining, Preparation and Properties." By A. E. Williams. 

Min. J. (Lond.), 1948, 230, 238^12. 
" Quarrying Fullers' Earth." Mine Quar. Eng., 1957, 23 (8), 326-335. 
" Bleaching Clay." By A. D. Rich. " Industrial Minerals and Rocks." Amer. Inst. Min. Met. 

Petrol. Engnrs., 3rd Ed., 1960, pp. 93-101. 
" Clays." U.S. Bur Mines. Minerals Yearbook (Annual). 


The name garnet is used to designate a group of silicate minerals which are closely 
related and, although bearing much resemblance in physical properties, may differ 
rather widely in chemical composition. Their only use other than as gemstones is 
as abrasives. Some properties of garnets which have been so used are shown in 
Table 75. 

Table 75 

Some Properties of Garnets 


Variety of Silicate 




Almandine . 


3FeO . Al 2 O a . 3SiO a 






3MgO . Al 2 O a . 3Si0 2 




Rhodonite . 





Andradite . 


3CaO . Fe 2 O s . 3SiO a 




Spessartite . 


3MnO . A1 2 3 . 3SiO a 




Uvarovite . 


3CaO . Cr 2 3 . 3SiO a 






3CaO . Al 2 O s . 3Si0 2 




Of the above garnets, almandine is the chief industrial variety. 

Garnets are chiefly found in metamorphic rocks, particularly mica schists and 
gneisses. The proportion of garnet in the rock varies considerably but, as a general 
rule, it is not remunerative to treat rock which contains less than 10 per cent. 
Individual garnets may vary in size between microscopic crystals, and masses weigh- 



ing up to 100 lb. : those found in rocks are usually in more or less rounded form. 
They also occur in alluvial deposits which have resulted from the weathering of the 
parent rock, but in some cases the crystals are too small to be of industrial value. 

Garnet is usually subjected to a certain amount of dressing at the mine, such as 
hand cobbing for large masses, or crushing and concentration for the recovery of 
disseminated crystals. Concentration may take the form of wet or dry methods. 
Much of the final crushing and grading is done by buyers at their own plants. As the 
chief use for industrial garnet is as an abrasive, its physical properties are the deter- 
mining factors. 

World Production 

The chief producer of marketable garnet is the United States, whilst small 
tonnages are obtained from Japan, Canada, Egypt, Madagascar, the Argentine, 
Spain, Tanganyika and India. No reliable statistics are available for the total produc- 
tion, but it probably amounts to about 25,000 long tons. The output in the United 
States rose from a few tons in 1938 to 12,663 long tons in 1954, but fell to 10,985 
long tons in 1958. 

The chief producing States are New York, Idaho, California and Florida, the 
output being obtained mostly from deposits mined primarily for garnet. 


About 90 per cent, of the garnet used in industry is employed for the manufac- 
ture of garnet paper and cloth, the remainder being used in the form of loose grains. 
Garnet is usually offered for sale in a series of standardized grades which range from 
20-mesh to 200-mesh. 

Garnets vary considerably in colour, hardness, toughness and fracture and for 
abrasive purposes should have a hardness of at least 7-5 and preferably higher; on 
crushing, it should break sharply into angular fragments with round or curved 
edges (as thin slivery pieces are objectionable); it should be capable of being broken 
down to pea size to give a clean product, free from embedded impurities, and also 
of giving a full range of sizes between 20 and 200-mesh with only a small proportion 
of fines. Large crystals that have been badly shattered or weathered, or contain 
embedded impurities, are likely to crumble to dust on crushing. Granular garnet is 
rarely of value as an abrasive as it mostly breaks into rounded fragments. 

It is claimed that the toughness, fracture and colour of iron garnets can be 
improved by heating them to 800° C. for about twelve hours and then quenching. 
This process is used by several manufacturers in the United States. 

The efficiency of garnet for abrasive purposes cannot be ascertained solely by 
any standardized series of tests; behaviour under working conditions being the 
final criterion. 

It is desirable that the grains of crushed garnet intended for use on paper or 
cloth should have a high capillary attraction so that the glue will cover them com- 
pletely and adhere to them when they are attached to the backing material. For 
abrasive use, colour is not an important factor, but most trades insist on a deep red 



Garnet paper is used for finishing the surface of hard wood, before varnishing, 
for scouring leather soles and heels in boot and shoe manufacture, and in finishing 
articles made of hard rubber, celluloid and some plastics. In the metal working 
industry, garnet is used in finishing brass and metal furniture, for grinding valves 
and finishing castings. 

In recent years, some makers have produced " Electro-coated " garnet papers 
which are claimed to be particularly efficient. These papers are made by dropping 
the crushed garnet through an electrostatic field in which the wet paper acts as one 
electrode. This treatment causes the grains to orientate themselves with their points 
towards the highly charged electrode (which is suspended above the paper) and 
their butt ends to the paper. This ensures that the sharp splinter ends of the garnet 
are in the best position for abrasive work. 

Loose garnet powder may be used for polishing marble, slate or soapstone and 
in some sandblast work (particularly in the U.S.A.). 

Some garnet is made into abrasive wheels by the cementing process, but its low 
melting point prevents it being set with a ceramic bond. Garnet has been suggested 
for use in the manufacture of ferrites. 


" Mining, Concentration and Marketing of Garnet." By F. E. Wormser. Eng. Min. J.-Press, 1924, 

118 (No. 10), 525-31. 
" Garnet: Its Mining and Utilization." By W. M. Myers and C. O. Anderson. 17.5. Bur. Mines, 

Bull. 256, 1925, 51 pp. , „ „ „ T ,,„ 

" Abrasives." Part 3. " Garnet." By V. L. Eardley-Wilmot. Canad. Dept. Mines, Bull. No. 677, 

1927, 69 pp. 
" Abrasives." Anon. Min. Res. of the Br. Empire and Foreign Countries, Imperial Institute, Lond., 

1929, (Garnet, pp. 29-36.) 
" Garnets." By L. Aitkens. U.S. Bur. Mines, Inform. Circ. No. 6518, 1931. 
" Non-Metallic Minerals." By R. B. Ladoo and W. M. Myers. New York, 1951. (Garnet, pp. 

241-9, including bibliography.) 
" Garnets enter Electronics." Electronics (Business Edition), 1957, 30 (June 20th), 30. 
" Abrasives." By R. B. Ladoo in " Industrial Minerals and Rocks." Amer. Inst. Min. Met. and 

Petrol. Engnrs., New York, 1960, 3rd Ed., pp. 1-21. 
" Abrasives." U.S. Bur. Mines. Minerals Yearbook (Annual). 
" Garnet." By H. P. Chandler. " Mineral Facts and Problems." U.S. Bur. Mines Bull. 585, 

1960, 5 pp. 

Germanium and Gallium 

The principal mineral in which germanium is an essential constituent is germanite, a 
rather complex sulphide which also contains copper, iron, zinc and gallium. The 
germanium content varies between 5 10 and 10 19 per cent, and that of gallium may 
range up to 0-75 per cent. The only known deposit of germanite occurs at the 
Tsumeb copper mine, in South- West Africa, which also yields enargite, a sulphar- 
senate of copper which often contains some germanium. Germanium is also a 



constituent of the rare mineral argyrodite, Ag 8 GeS 6 , and has been reported to occur 
in zincblende, calamine, pyrites, euxenite, cassiterite and ores containing tantalum 
and columbium, but the amounts recorded are all small, usually about 001 per 
cent, or less. 

A germanium-bearing mineral named renierite, having the composition (Cu . 
Fe) 3 (Fe.Ge.Zn.Sn) (S.As>4, occurs in the Belgian Congo and chemical analyses 
show it to contain from 6-37 to 7-80 per cent, germanium. This mineral occurs at 
the Prince Leopold mine at Kipushi and is the source of the germanium produced 
from the flue dust at the Kolwezi smelter. 

Although gallium occurs in the earth's crust in approximately the same propor- 
tion as lead, about 15 gm. per ton, the latter is more favourably concentrated in 
deposits. In addition to being found in germanite, gallium has also been recorded in 
certain zinc and manganese ores, iron pyrites, bauxites, china clay and in com- 
mercial aluminium. Zinc concentrates produced in the Joplin district, Mo., U.S.A., 
are said to carry 3-5 oz. per ton. The metal has also been recovered in Sardinia, 
Italy, from electrolytic zinc refinery residues, which contained up to 015 per cent., 
accompanied by about 0-06 per cent, of germanium. 

Both germanium and gallium have been found in many coal ashes and, at one 
time, ash from power-plants using some Durham and Northumbrian coals was 
exported to Germany and there used as a source of these metals. Such ash now 
constitutes the sole source of supply of germanium in Great Britain. 

World Production 

No reliable statistics are available concerning the production of germanium or 
gallium in recent years. An estimate by the U.S. Bureau of Mines puts the world's 
production of germanium in 1957 at 90,000 lb., but since that year production has 
increased considerably. 

The extraction of gallium from flue dusts containing 0-1-1 -5 per cent, gallium or 
from gas liquors containing 10- 2 -10" 3 per cent, has been recorded from Japan. 
In 1957 the Hungarian Metal Research Institute developed a process for obtaining 
gallium metal from the alkaline lye remaining after the extraction of alumina from 
bauxite by the Bayer process. 

It is stated that the Aluminium Ore Company, a subsidiary of the Aluminium 
Company of America, is recovering about 1 oz. of gallium from each ton of bauxite 
treated for the extraction of alumina and that the element has been shown to be 
present in liquors obtained during the treatment of bauxite in Great Britain, to the 
extent of 0-5 gm. per litre. Germanium is also present in the crude aluminium pro- 
duced and if this is refined by the Hoffe-Frary process, the germanium may. be 
recovered as an alloy with copper, silicon and iron containing 01 to 0-2 per cent of 
the metal. Gallium is also being produced in the United States by the Anaconda 
Company at Great Falls, Mont., and by the Eagle-Picher Company at Joplin, Mo. 

According to A. R. Powell, gallium has been recovered by Johnson, Matthey & 
Co. Ltd. of London by a solvent extraction process from the residual liquors 
remaining after the distillation of germanium tetrachloride from solutions obtained in 
the treatment of flue dusts and germanite ore. 




Germanium falls into the intermediate category of elements between the metals 
and non-metals, and has chemical resemblance to both arsenic and silicon. It is 
usually referred to as germanium metal and has a high electrical resistivity, expands 
on solidification and has anti-corrosive properties. Some of the physical properties 
of pure metallic germanium are as follows: 

Atomic number 

. 32 

Atomic weight 

. 72-59 

Melting point 

. 958-5° C. 

Boiling point 

. 2,700° C. 

Crystal structure 

. Octahedral 

Thermal neutron cross section absorption. 2-8 barns 

Isotopes (stable — relative abundance) . Ge-70, 20-4 per cent.; Ge-72, 27-4 per 

cent.; Ge-73, 7-8 per cent.; Ge-74, 
36-6 per cent. ; Ge-76, 7-8 per cent. 

Density (at 25° C.) 5-32g/cc. 

Intrinsic resistivity at 27° C. . .47 ohm/cm. 3 


In the United States both germanium and gallium are extracted from flue dusts 
and sludges obtained during the smelting and refining of zinc, whereas in Great 
Britain the metals are recovered from certain flue dusts resulting from the industrial 
utilization of coal 

In recent years important work has been carried out in Great Britain on the 
extraction of metallic germanium of a high degree of purity by Messrs. Johnson, 
Matthey & Co. Ltd., working in association with the General Electric Co. Ltd. and 
the British Thomson-Houston Co. Ltd., the last-named concentrating their attention 
principally on the question of the utilization of the metal produced by the first- 
named firm. 

In the earlier work the raw material used as the source of the metal was the 
flue dusts obtained from producer gas plants using coke made from coals mined in 
the Northumberland and Durham coalfields; these coals contained about 003 
per cent, of germanium and about the same amount of gallium. Later, however, it 
was found that most bituminous coals from the Midland, Scottish and some of the 
Yorkshire coalfields contain higher percentages of germanium than those from 
Northumberland and Durham. When the coals are coked, the rare elements remain 
with the coke and when this is used in producer gas plant most of the gallium and 
germanium is volatilized with the gas, probably as sulphides or lower oxides. If the 
gas is cooled before being burned, the bulk of the rare elements is deposited in the 
form of a black dust containing 30-70 per cent, of carbon and many metallic 
constituents. If, however, the gas is burned while still hot, the metallic constituents 
are converted to oxides, which are deposited in the cooler parts of the flue system 
and it is this type of deposit which provides the richest source of gallium and 
germanium in Great Britain. 



Analyses of three typical flue dusts as given by A. R. Powell (/. appl. Chem. 
1951, 1, 542), are shown in Table 76. 

Table 76 

Typical Analyses of Flue Dusts. 
Per cent. 







Silica, Si0 2 




Alumina, A1 2 3 




Ferric oxide, Fes,0 3 




Zinc oxide, ZnO 




Lime, CaO 




Magnesia, MgO 




Alkalis, Na 2 + K 2 




Water, H a O . 




Lead oxide, PbO . 




Copper oxide, CuO 




Arsenic, As 2 O s 




Molybdic oxide, MoO a 




Nickel and cobalt oxides, NiO 

+ Cob 




Phosphoric anhydride, P 2 5 




Titanium dioxide, TiO a . 




Vanadic oxide, V 2 O s 




Sulphuric anhydride, SO a 




Sulphur (as sulphide), S . 




Chlorine, CI . 



1 95 

Carbon, C 




Gallium oxide, Ga a 3 




Germanium oxide, GeO s 









O = CI + S 


Owing to the number of metallic constituents in flue dust the extraction of 
germanium and gallium is a complicated process. For details of the process and 
flow sheets the very comprehensive article by A. R. Powell, F. M. Lever and R. E. 
Walpole should be consulted. 

In the method used for recovering germanium from the American Tri-State zinc 
ores the sulphides are roasted to convert them to the oxides, which are next sintered 
with sodium chloride, whereby the germanium, together with some cadmium and 
other metals, is volatilized as the chloride. The vapours are condensed and lead 
removed from the fume as lead sulphate after leaching with sulphuric acid. The 
addition of zinc dust to the solution precipitates germanium, copper and arsenic, 
but the cadmium remains in solution. The impure germanium precipitate is refined 
by the tetrachloride process. 

In the Belgian Congo germanium occurs as the mineral renierite associated with 
copper ore. The dust obtained during the production of copper matte and blister 
copper contains between 0-2 and 0-4 per cent, of germanium and about 7 per cent. 



of arsenic. These dusts are processed at Oolen, Belgium. In the method used the 
dusts are pelleted and heated in a reducing atmosphere of hydrogen and carbon 
monoxide in a vertical retort at 800° C. About 90 per cent, of the germanium 
sulphide is volatilized with only 5 per cent, of lead sulphide and the vapours con- 
taining these compounds can be burnt in air to give the oxides, which are then 
ready for separation and purification of the germanium. 

At Tsumeb in South-West Africa germanium is obtained as a by-product in the 
extraction of copper from complex copper-lead-zinc-arsenic ores, a special process 
having been devised for this purpose. The by-product containing a few per cent, of 
germanium is exported to the United Kingdom and the United States. 

Since the correct working of the germanium diode depends essentially upon the 
presence of small (but controlled) amounts of known impurity elements, it is neces- 
sary, before these elements are added, to start with very high purity germanium and 
to achieve this end the process of zone refining is used. In this process an ingot of 
germanium metal contained in a crucible is placed in a long quartz tube in an atmos- 
phere of hydrogen. The tube is surrounded at intervals by three R.F. heating coils, 
which are arranged to travel together slowly from one end of the ingot to the other, 
thus causing three molten zones, each about 1 in. long, to move along the bar in one 
operation. Any impurities present tend to remain in the liquid metal rather than 
move across the liquid/solid interface at the trailing end of the zone, and this results 
in their being swept to the end of the bar. The presence of impurities is detected by 
resistivity measurements made along the axis of the bar and they can be removed, 
therefore, by cutting off the end at a suitable point, thus leaving metal of the purity 

In the method of refining germanium, described by the Hackbridge & Hewittic 
Electric Co. Ltd. of Walton-on-Thames, England, in order to produce single 
crystal metal, the germanium is first melted in a cup-shaped quartz crucible by means 
of an R.F. heating coil supplied at 400 kc. per sec. A long, thin piece of specially 
prepared single crystal germanium (the seed) is then lowered into the surface of the 
molten metal. Temperature is controlled so as to be high enough to melt the tip of 
the seed and low enough for the meniscus of liquid germanium to be held up from the 
molten metal by surface tension. When a sufficient diameter of solidification has 
formed round the tip of the seed, it is slowly and continuously raised, resulting in a 
growing column of solid germanium being pulled up from the melt and left hanging 
from the seed as a single large crystal. The operation is carried out in an atmosphere 
of specially dried high purity hydrogen. The introduction of antimony to produce an 
n-type crystal is done during the crystal growing by adding to the crucible a care- 
fully calculated amount of this metal. The completed crystal is shaped into a square 
sectioned stick and cut into 0-03 in. wafers by means of a diamond saw. Both 
surfaces are then lapped to bring the thickness to 0-02 in. At this stage the rectifying 
junction is made. On one side of a disc of n-type single crystal germanium a slightly 
smaller disc of indium is placed and the whole raised to a temperature greater than 
the melting point of indium (155° C), but less than that of germanium (980° C). The 
germanium and indium wafers are loaded and jigged in graphite blocks in batches 
and alloyed inside quartz tubes in an atmosphere of hydrogen. The liquid indium 



dissolves germanium up to saturation point, and upon cooling, the dissolved 
germanium precipitates out of solution and recrystallizes back on to the base 
germanium. This recrystallized layer of germanium on the face of the disc now 
contains a larger number of indium atoms than it did originally of antimony atoms, 
and has been converted to p-type, so that it forms a rectifying junction with the 
n-type base germanium. A detailed account of zone refining has been given by 
N. L. Parr in a monograph on the subject published by the Royal Institute of 


Germanium. During World War II research work carried out at Purdue Uni- 
versity showed that high inverse-voltage rectifiers could be produced from metallic 
germanium and such rectifiers were used in many types of circuit applications at 
frequencies of 30 Mc/s or less, such as second detectors in wide band receivers, 
direct current restorers and diode modulators. It is essential that the metal for this 
purpose shall have a high purity, particularly in regard to its arsenic content, which 
must be less than 0-1 part per million. 

Rectifiers using germanium came into prominence during World War II, when it 
was found that when the length of the wave for wireless transmission was shortened, 
in some instances the ordinary thermionic valves became unsuitable and that the old 
" cat's whisker " type was better. Later, it was found that a crystal of pure ger- 
manium with two-point contacts placed close together could act as a triode, as 
amplifier or oscillator. Such valves are now called " transistors." 

Germanium is finding increasing use in the electrical industry as a power rectifier. 
The outstanding advantage claimed is that a high efficiency, low cost, rectifying unit 
can be obtained for operation at the lower voltages. The forward voltage drop of a 
single germanium cell is only about 0-5 volts, so that although the reverse voltage is 
much less than that of the mercury arc, extremely high efficiencies are obtainable at 
quite low voltages. At the present time equipments can be built at a competitive 
price up to around 300 volts D.C., but the most effective field for germanium appears 
to be in the low voltage range from 8-150 volts. The germanium rectifier does not 
object to low temperature, but breaks down at somewhere about 80° C. Accordingly 
it is necessary to provide adequate cooling. 

In general semi-conductors may be described as materials in which electrons 
flow only to a limited extent and in one direction more easily than in others. The 
two elements which at present are most important as semi-conductors are ger- 
manium and silicon. Two types of conductivity are possible in a semi-conductor, 
positive (p-type) and negative (n-type). A deficiency of electrons in the crystal 
lattice of the semi-conductor, caused by the presence (as impurities) of Group III 
elements (e.g. boron or aluminium), gives rise to p-type conductivity. An excess of 
electrons, owing to the presence of Group V elements (e.g. phosphorus or arsenic), 
results in n-type conductivity. The amounts of impurities concerned are only one 
or two parts in 10 9 by weight. 

The basis of all devices designed to make use of the special properties of semi- 
conductors is the junction of p-type and n-type regions of conductivity. Provided 



suitable metals are used, junctions are always created at the contacts attached to 
single crystals; junctions can also be made within a single crystal by doping 
different parts of it with appropriate impurities. Depending on their design, these 
devices behave in much the same way as simple thermionic diodes and triodes, that 
is to say they will (a) allow current to flow in one direction only (rectify), or (6) 
permit the control of relatively large currents flowing in a circuit by fluctuations in 
a minute current flowing in an associated circuit (amplify). 

At the present time there are three general types of semi-conducting devices in 
commercial production, (1) rectifiers; (2) solar energy converters; (3) transistors. 

Germanium rectifiers are now in use in many industries in connection with 
electroplating, battery charging and in the control of sintering furnaces and power 
plants. Diode and triode germanium transistors are also used in television, radio, 
hearing aids, guided missiles, aircraft control apparatus and telephone equipment. 

In the solar energy converter, photons from the sun are utilized to induce a direct 
current in a p-n structure so that the sun's energy is used to create a direct current 
without first going through a thermal or mechanical cycle. The present day cost of 
such solar energy converters is prohibitive for most commercial purposes, except 
under exceptional conditions, but a small pole-mounted telephone exchange has 
been operated successfully. With silicon the maximum conversion efficiency of solar 
radiation into electrical energy is about 22 per cent. ; similar devices using germanium 
would have about half this efficiency. 

Germanium is the active component of p-n photo-electric cells, which are very 
small and robust and have characteristics similar to those of vacuum and gas-filled 
cells, but are more sensitive to tungsten filament light. 

Germanium has been suggested for addition to aluminium and magnesium alloys 
to improve their strength and rolling properties. The sulphide has been used 
experimentally as a hydrogen catalyst. 

An alloy of gold containing 13 per cent, of germanium melts at 357° C. and 
expands on solidification. Magnesium germanite has been used as a phosphor in 
fluorescent lamps. 

Gallium. This metal, on account of its low melting point (29 -4° C.) and its high 
boiling point (about 2,000° C), has found use in special purpose thermometers 
which will function up to 1 ,000° C. 

Gallium has been suggested for coating optical mirrors. 

Alloys of very low melting point can be made by the addition of gallium to 
quaternary alloys containing tin, bismuth, lead and cadmium. The percentage 
compositions of several such alloys are as follows : 






Melting Points 

















" New Occurrences of Germanium: The Occurrence of Germanium in Silicate Minerals." By J. 

Papish. Econ. Geol., 1929, 24, 470-80. 
" Germanium in Relation to Electrolytic Zinc Production." By U. C. Tainton and E. T. Clayton. 

Trans. Electrochem. Soc, 1930, 57, 279-88. 
" Cadmium, Thallium, Indium and Gallium as By-products of the Lithopone Industry." By 

W. N. Hirschel. Chem. and Ind., 1933, 797-8. 
" Review of the Electrochemistry of Gallium." By H. C. Fogg. Trans. Electrochem. Soc, 1934, 66, 

" Germanium and Gallium in Coal Ashes and Flue Dust." By G. T. Morgan and G. R. Davies. 

Chem. and Ind., 1937, 56, 717-21. 
" Das Gallium." By E. Einecke. Leipzig, 1937, 155 pp. 
" Gallium." Part II. " Extraction of Gallium and Germanium from Germanite." By F. Sebba 

and W. Pugh. /. Chem. Soc, 1937, Pt. 2, 1371-3. 
" Gallium." Part III. " The Electrodeposition, Purification and Dissolution of Gallium." By 

F. Sebba and W. Pugh. /. Chem. Soc, 1937, Pt. 2, 1959-62. 
" The Occurrence and Some Uses of Gallium and Germanium." By G. Oldham. Min. J. (Lond.), 

1946, 226, 89. 
" Technology of Germanium." By R. I. Jaffee, E. W. McMullen and B. W. Gonser. Trans. 

Electrochem. Soc, 1946, 89, 277-90. 
"Germanium and Its Compounds: Extraction and Recent Applications." By A. G. Arend. 

Industr. Chem., 1947, 23, 77-82. 
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Non-ferrous Metals." Inst. Min. Met., Lond., 1950, pp. 51-66. 
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(Feb.), 91-4, including flowsheet and bibliography. 
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R. E. Walpole. /. Appl. Chem., 1951, 1, 541-51, including bibliography and flowsheets. 
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and J. R. Musgrave. /. Metals, 1952, 4, 1 132-7, including flowsheets and bibliography. 
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" Etudes sur le Gallium, en vue de son Extraction au Course de la Fabrication de l'Alumin." 

By P. de la Breteque, Lausanne 1956, 148 pp. 
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" Transistor Technology." Ed. by H. E. Bridgers, J. H. Scaff and J. N. Shive. 3 vols., N.Y., 1957 
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Metals," Inst. Min. Met., 1957 [Gallium, p. 28]. 
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Hewittic Electrical Co., Walton-on-Thames, England, 1958, 7 pp. 
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1958, 48, No. 3, 114-18. 
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Walton-on-Thames, England, 1959, 11 pp. 
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1960, 4 pp. 
" Minor Metals." U.S. Bur. Mines, Minerals Yearbook. (Annual) 



Gold occurs widely distributed in minute quantities throughout the earth's crust, 
usually native and associated with silver in proportions which may vary between 
about 1 : 10,000 in some silver-lead ores and 10 : 1 in some Australian gold ores. 
Gold is also present in sea-water to the extent of about 0-5-1 -0 gr. per ton. 

The sources from which gold is generally obtained are, (1) quartz veins and lodes 
in certain rock formations, (2) from " placers " (alluvial deposits) in ancient or 
modern stream beds, (3) from deposits worked primarily for other metals, such as 
copper, lead, silver and nickel, the gold being obtained as a by-product. 

The only known natural compounds of gold with other elements are the tellu- 
rides, such as calaverite and krennerite (Au.Ag)Te2, sylvanite (graphic tellurium), 
nagyagite (a sulpho-telluride of gold and lead) and kalgoorlite, HgAu2Ag2Te6. Most 
of these minerals have been found and worked in W. Australia, California and 
Colorado, but are comparatively rare elsewhere. 

Native gold usually contains more than 99 per cent, of Au + Ag and less than 1 
per cent, of copper, iron, etc. Placer gold is usually more pure than that derived 
from lodes. 

The most productive goldfields are those of the Witwatersrand in the Union of 
S. Africa, where the gold occurs in " banket," a coarse conglomerate of quartz 
pebbles with a metamorphozed matrix. 

In view of the diversity of factors influencing the remunerative mining of gold 
ores, it is not possible to state what content of gold will render the working of a 
deposit economically possible. The following figures, however, concerning the S. 
African gold industry may be of interest in relation to large scale underground 
mining operations. In 1958 over 65J million tons of ore milled had an average grade 
of 5-228 dwt. per ton. The working cost per ton milled averaged 46s. lid. per ton, 
whilst the revenue amounted to 65s. 9d. per ton, giving an estimated working 
profit from gold of 18s. lOd. per ton. In addition, however, the gold mines benefited 
from their recovery of uranium and thorium from the waste, which in 1956 
amounted to £37,742,059. 

World Production 

The world's production of gold in 1958 was estimated to total about 30 million 
fine troy ounces, excluding the output from the U.S.S.R., which has been variously 
estimated between 2 and 18 million troy ounces. Gold produced in British countries 
totalled over 25 million fine troy ounces, or nearly 84 per cent, of the Free World 
output. The largest productions were recorded from the Union of S. Africa, Canada, 
the United States, Australia, Ghana, S. Rhodesia, the Philippines, the Belgian 
Congo, Mexico, Columbia, Japan, Nicaragua and India. No gold ore is mined in the 
United Kingdom, whose imports in 1958 (in terms of fine troy ounces of metal 
content) were ore, etc., 45,000; unrefined bullion 1,542,497; refined bullion 
22,460,998, and coin 436,000. In the same year the United Kingdom exports 
included refined bullion 10,738,067; and coin 564,000 fine troy ounces. 



Extraction of Gold 

The methods of recovery of gold from alluvial, or placer deposits, compacted 
sands, gravel and any loosely coherent detrital beds, vary from primitive hand- 
washing in streams, dry-blowing and hydraulicking, to the very elaborate gold 
dredges which can treat large quantities of material at a low cost and with only a 
small consumption of water. 

Gold is usually recovered from the concentrates obtained by alluvial working by 
agitating them with mercury. The resultant solid amalgam, which may contain from 
30-45 per cent, of gold and silver, is subsequently retorted to distil off the mercury. 

The treatment of conglomerate gold ores, such as those obtained by deep level 
mining on the Rand, varies in detail according to the nature of the ore. In general, 
however, it may be said to comprise (1) fine crushing of the ore, frequently in tube 
mills; (2) removing the coarser gold by amalgamation with mercury; (3) sizing to 
remove fines; (4) extracting the gold and silver by means of a solution of a cyanide, 
usually potassium cyanide of about 06 per cent, strength; (5) recovering the gold 
by passing the cyanide solution over zinc shavings or zinc dust; (6) treating the zinc- 
gold precipitate with acid to dissolve the zinc, calcining and smelting the residue in a 
reverberatory furnace. 

The potassium cyanide solution employed usually amounts to 25 or 30 per cent, 
of the weight of the ore. During the treatment, which lasts from 4-7 days, the sand is 
permitted to drain as frequently as possible to allow the entry of air, but aeration 
may be effected by injecting air under pressure. 

Recently processes have been devized for the separation and recovery of gold, 
silver and nickel from alkaline cyanide solutions by ion exchange methods. 

Some of the physical properties of pure gold are as follows: 

Atomic number 

Atomic weight 

Specific gravity 

Melting point 

Boiling point 

Thermal conductivity 

Coefficient of linear expansion (0-100°C.) 

Specific heat (at 20° C.) 

Latent heat of fusion 

Thermal neutron cross-section absorption 

Electrical resistivity (at 20° C.) 

Temperature coefficient of resistance (0-100°C.) 

Ultimate tensile strength (annealed) 

Elongation (annealed) . 

Modulus of elasticity in tension 

Modulus of elasticity in torsion 

Vickers hardness (annealed) . 




1,063° C. 

2,530° C. 

0-70 cm./g./sec. 

0-000014 per °C. 

031 cal./g./°C. 

16-1 gm./cal. 

95 barns 

2 -4 microhms/cm. 3 


7 tons p.s.i. 

70 per cent. 

10-3 x 10 6 p.s.i. 

3-8 X 10 6 p.s.i. 


The properties which distinguish gold from most other metals are (1) that no 
oxide film is formed when it is heated in air up to and beyond its melting point, and 



(2) its greater malleability and ductility than any other metal at ordinary tempera- 
tures. It is harder than silver and softer than tin, but its hardness varies with its 
physical condition, i.e. whether cast, rolled or annealed. 

Gold is not attacked by any of the mineral acids alone, but is readily soluble in 
aqua regia, or in any mixture of acids producing nascent chlorine, and almost any 
chloride will dissolve gold in the presence of an oxidizing agent. It is, however, 
soluble in strong sulphuric acid if a little nitric acid is added. It dissolves in hydro- 
chloric acid in the presence of certain organic substances, e.g. methyl or ethyl alcohol, 
chloroform or glycerol. It is not affected by the normal alkalis, but alkali cyanides, 
particularly in the presence of oxygen, rapidly dissolve gold. Its optical properties 
make it of value both as a reflector for infra-red rays and as a filter when coated on 


Coinage. At one time gold coins were extensively used for currency proposes, but 
since about 1933 they have been withdrawn from circulation by most countries, and 
gold's chief monetary function (in the form of bullion) is as a reserve to give stability 
to paper currency and for the settlement of international balances. Gold coins are 
still produced at the British Mint, but not for circulation in the United Kingdom. 
The British Gold coinage alloy contains 916-6 parts of gold, 83-3 parts of copper per 
1,000 parts at 949° C. 

Jewellery. The popularity of gold for jewellery may be largely explained by its 
attractive colour, and freedom from atmospheric corrosion. The colour of gold is 
normally yellow, but white, green, blue, red, and purple can be produced by alloying 
it with other metals. Varying proportions of silver, copper, nickel, palladium or zinc 
give white gold, alloying with cadmium produces a green metal, iron gives blue and 
aluminium a purple metal. 

" Rolled gold " finds most use in the fancy jewellery trade. It is produced when 
bars of alloyed gold and a base metal (usually brass) are sweated or soldered to- 
gether and then rolled. During rolling the gold and base metal undergo the same 
reduction and so their ultimate thickness is in the same ratio as originally. The 
thickness of gold may reach 0003 in. and may be 10-, 14- or 18-carat quality. 

A number of gold alloys are used in the jewellery trade and are usually designated 
by their " carat " number, i.e. parts of gold in 24 parts of the alloy (9, 14, 18, 22 
carat). A wide variety in the relative percentages of the base metals present is 
possible. Thus, 9-carat gold may contain silver, copper, zinc, cadmium, nickel and 
occasionally iron, according to the particular colour and properties desired in the 
finished article. 22-carat gold alloys, commonly known as standard gold, were the 
early legal standard for gold coins and were later legalized for jewellery and gold- 

Gold thread is manufactured on a fairly extensive scale in India by the electro- 
lytic deposition of gold on metallic wire, which may be flattened silver wire or 
copper wire electro-coated with silver, silk or cotton yarn coiled with silver wire 
and termed " lametta." 

Gold leaf, produced by hammering pure gold to considerable thinness, is used 



for coating picture frames, book edges, the hair springs of marine chronometers 
and galvonometers. It can be produced as thin as 5-millionths of an inch, 1 oz. of 
which would cover 250 sq. ft. 

Electrodeposited Gold. Although gold is a relatively soft metal, electrodeposited 
coatings are extensively employed for the protection of many instruments against 
corrosion. Examples include the cans used to house amplifiers in the latest trans- 
Atlantic cable. Formerly, tinplating was used, but this had a tendency to grow 
whiskers. The beryllium-copper leads for valves used in the same cable are gold- 
plated before being braided. Electrodeposited gold is used as an alternative to 
rhodium plating on radio-frequency conductors, where the basis material is not very 
suitable for the deposition of rhodium. Gold plated molybdenum wire is used in the 
construction of radio valve grids to reduce secondary emission. 

A method for gold plating without electrodes has been evolved by Baker & 
Co., New York and London, who by their " Atomex " process can deposit 24-carat 
gold by ionic displacement on some base metals, e.g. copper, nickel or steel. The 
deposits are claimed to be very hard and dense. 

Gold films deposited on bismuth oxide base layers have a high electrical con- 
ductivity and optical transmission in the visible region. They also have high reflec- 
tivity in the infra-red and hence are valuable as windows and reflectors of solar 
radiation in aircraft, etc. 

Electrical and Electronic Engineering. As a contact material its complete freedom 
from atmospheric tarnish has led to the use of gold where constant contact resistance 
is of importance. For many electronic applications electrodeposited gold is employed , 
but its inherent softness and tendency to stick have limited its field and generally one 
of its alloys is used. The 30 per cent, silver-gold alloy is sometimes employed in 
light duty relays, as is the 7 per cent, platinum, 26 per cent, silver and 67 per cent, 
gold alloy. The latter alloy is slightly harder, but both alloys show inferior resistance 
to electrical wear compared with platinum. Gold-clad phosphor bronze or nickel 
silver is also used for contact springs in radio-frequency circuits. For use as a rubbing 
or sliding contact advantage is taken of the hardness and good elastic properties of a 
copper-silver-gold alloy containing 62-5 per cent. gold. 

Radioactive gold provided a source of heat in an experimental thermionic 
converter developed by the General Electric Company (U.S.A.). 

An exceedingly thin gold coating on space-probing satellites provides a highly 
reflective surface that can withstand the temperature extremes encountered in outer 
space and protect delicate instruments from overheating. Gold has also been used 
for cladding the internal components of certain nuclear-power reactors using highly 
corrosive liquid fuel. 

Gold Clad Materials. Gold and many of its alloys can readily be applied and 
integrally bonded to base metal backings to provide a surface having the corrosion 
resistance of gold at a much reduced cost. Suitable spring materials may thus be 
prepared with an inlay of gold alloy to act as the contact surface. Gold-clad materials 
are also used in chemical engineering where a comparatively thin facing of gold 
alloy is employed on a base metal backing to provide a corrosion resistant surface. 

Chemical Engineering. Gold alloys are the principal materials of which the spin- 



ning jets used in the manufacture of viscose rayon are constructed. Alloys containing 
about 70 per cent, gold, with platinum or platinum and palladium, are amongst the 
most suitable for this purpose; they are extremely corrosion resistant, have excellent 
working properties and are capable of precipitation hardening by suitable heat 

Gold is used to a limited extent, either as sheet or as an electrodeposit, to form a 
protective lining in reaction vessels or autoclaves exposed to highly corrosive con- 

Advantage is taken of the corrosion resistance of palladium-gold alloys in the 
manufacture of laboratory crucibles and dishes. " Palau," a 25 per cent, palladium- 
gold alloy can be used as an alternative to platinum where conditions permit. 
This alloy has a melting point of 1,380°C. and compares with platinum in its 
resistance to attack by mineral acids and by fused sodium carbonate, but is not 
suitable for bisulphate fusions. 

A process developed in Germany during World War II utilized gold for the re- 
covery of platinum catalysts from the waste gases evolved during the manufacture of 
nitric acid by the oxidation of ammonia. The hot gases were passed through a bed of 
gold plated ceramic rings and the fine platinum carried in the gases became alloyed 
with the gold, which was subsequently stripped from the rings and refined. 


A large number of gold alloys have been prepared and investigated, those which 
have found most industrial use are the binary alloys with silver, palladium and 
platinum and the ternary alloys with platinum and silver, and copper and silver. 
Silver-gold alloys are ductile and easily fabricated into normal commercial forms. 
The addition of silver reduces the tarnish resistance of gold, but all alloys containing 
more than 50 per cent, of gold by atomic proportions may be regarded as similar to 
gold in this respect. The most widely used platinum-gold alloy is one containing 
30 per cent, of platinum, which has a hardness of 100 Vickers in the annealed 
condition and can be heat-treated to obtain values up to 250 Vickers, a property 
which makes it useful for the spinning jets used in artificial silk manufacture. 
Platinum-gold-silver alloys have been developed commercially as substitutes for 

The standard alloy used for dentistry up to about thirty years ago was 20-carat, 
containing 83 -3 per cent, of gold. The modern practice is to employ alloys containing 
gold, silver and copper, with possibly some platinum, palladium or zinc, and even 
tin and nickel. It is stated that the addition of platinum reduces risk of fracture and 
acts as a hardener to the gold. 

Gold is an important constituent of some copper-gold brazing filler metal 
compositions, which are described under A.S.T.M. Tentative Specification B 
260-52 T, which specifies the chemical composition shown in Table 77. 

The above alloys are used principally for joining parts of electron tube assemblies 
where gaseous inclusions are particularly objectionable. For electron tubes they are 
usually applied by induction, furnace, or resistance brazing in a reducing atmosphere 
or in a vacuum, without a flux. 



Table 77 

Copper-Gold Brazing Filler Metal— A.S.T.M. B 260-52T 


Per cent. 

Per cent. 



Per cent. 






Range °F. 

BCuAu-1 . 
BCuAu-2 . 








* These alloys shall not contain more than 0005 per cent, volatile impurities, such as 
zinc or cadmium, and should be available oxygen-free if so specified by the purchaser. 

Gold is a primary constituent of the recently improved " Pallador " thermo- 
couple which is claimed to have a much greater response than the well-known 
platinum/rhodium-platinum combinations and to be free from the oxidation 
problems associated with base metal thermocouples. The " Pallador " thermocouple 
which can be used for temperatures up to 1,000° C, consists of a 40 per cent, 
gold-palladium alloy wire and one of 10 per cent, indium-platinum. 

A corrosion-resistant gold-beryllium alloy suitable for use in nucleonic reactions 
is produced by compacting the powdered metals for one hour at 350° C. A typical 
alloy described in U.S. Patent No. 2,558,523 of June 26th, 1951, contains beryllium 
8-45, gold 91 -55 per cent. 

Much of the above information regarding the industrial uses of gold and its 
alloys was taken from trade publications issued by Messrs. Johnson, Matthey & Co. 
Ltd. of London. 


" A Text-book of Rand Metallurgical Practice." By Ralph Stokes et al., 2 vols., Lond., 1926. 

" Gold Deposits of the World." By W. H. Emmons. N.Y., 1937, 562 pp. 

" The Metallurgy of Gold." By Sir Thomas Kirk Rose and W. A. C. Newman. Lond., 7th Ed., 

1937, 561 pp. 
" Gold." By D. M. Liddell. (Handbook of Non-ferrous Metallurgy.) N.Y., 1945, Vol. 2, pp. 

" Gold Metallurgy on the Witwatersrand." By A. King et al., Transvaal Chamber of Mines, 1949, 

458 pp. 
" Cyanidation and Concentration of Gold and Silver Ores." By J. V. N. Dorr and F. L. Bosqui. 

N.Y., 1950,511pp. 
" The Refining of Gold and Silver." By A. E. Richards. "The Refining of Non-ferrous Metals," 

Inst. Min. Met., 1950, pp. 73-118. 
" Treatment of Gold Ores in South Africa and Canada." By E. C. Ellwood. Trans. Inst. Min. 

Met., 1950-51, 60, 21-36. 
" Future Resources and Problems of the Witwatersrand Goldfield." By R. S. G. Stokes. Trans. 

Inst. Min. Met., 1953-54, 63, 457-73. 
" Gold, Engineering Properties and Uses." Johnson, Matthey & Co. Ltd. Lond. 1953, 12 pp. 
" The Recovery of Gold, Silver and Nickel from Alkaline Cyanide Solutions by Means of Weak- 
Base Ion Exchange Resins." By J. Alveston, D. A. Everest, N. F. Kember and R. A. Wells. 

/. App. Chem., 1958, 8, 77-86. 
" Gold." By P. Hagenmuller. Nouveau Trait6 de Chimie Minerale. Ed. by P. Pascal. Paris, 1957, 

Vol. Ill, pp. 647-822. 
" Noble Metal Thermocouples." Johnson, Matthey & Co. Ltd. Lond., 1956. 
" The Pallador Thermocouple." By H. E. Bennett. Platinum Metals Rev., 1960, 4 (No. 2), 66-7. 
" Gold," U.S. Bur. Mines, Minerals Yearbook. (Annual) 


American Society for Testing Materials 

A.S.T.M. Standards, 1958: 

Copper-Gold Brazing Filler Metal, B 260-52T. 



Graphite, also known as plumbago and black lead, consists of a crystalline form of 
elemental carbon, and is usually found associated with impurities such as quartz, 
calcite, silicate minerals, etc. 

In trade, the term graphite is often applied to the crystalline flake mineral, 
plumbago to the massive variety and black lead to amorphous material, such as is 
used for stove polish and similar purposes. 

Graphite has a specific gravity of 2-1-2-3, a hardness of 1, and is very resistant 
to the action of hydrochloric and hydrofluoric acids, chlorine, heat and many 
chemical reagents. It is a good conductor of electricity and heat. 

In commerce, the types recognized are crystalline, flake, massive and amorphous. 
The last named variety is not amorphous in the correct sense of the term, but 
consists of particles so small as to give a compact non-crystalline appearance to the 
mass. No one type of graphite is suitable for all purposes, the coarsely crystalline 
variety being the most valuable, but the amorphous type is the grade chiefly used in 
industry. As marketed, graphites, particularly the crystalline and flake varieties, 
are divided into several grades according to size and carbon content. Thus, Ceylon 
crystalline graphite is graded into (1) lump, ranging from the size of walnuts to that 
of peas ; (2) chip, from pea size down to about that of wheat grains ; (3) dust, from 40- 
to 60-mesh; (4) flying dust, which is finer than 60-mesh. The carbon content varies 
from about 98 to 90 per cent., for lumps, whilst chips may contain from 90 to 85 per 
cent., dust from 80 to 75 per cent., and flying dust from 85 to 50 per cent. 

The mineral, as mined, nearly always requires some form of concentration before 
it can be marketed. The treatment ranges through simple hand-picking to flotation 
and to magnetic and electrostatic processes. Some graphites can also be beneficiated 
by chemical treatment. Thus moistening with nitric acid causes certain graphites to 
swell and become easier to float from the gangue minerals. Other chemical processes 
used involve successive treatment with hydrochloric acid, caustic soda and hot 
water. It is claimed that by this treatment the graphite becomes more plastic and so 
very suitable for pressing into blocks or plates. 

According to German Patent 924,690 of March 7th, 1955, granted to H. Ulrich, 
natural graphite can be purified by heating it in gases capable of forming volatile 
products with the impurities. Thus, silica is removed by hydrofluoric acid, iron and 
other metallic oxides by heating in chlorine containing 1-5 per cent, by volume of 
carbon tetrachloride. 

Colloidal graphite dispersions are usually manufactured by grinding artificial 
graphite in the presence of a colloid, e.g. tannin, and then separating out the coarser 
particles by means of a flotation process. 

World Production 

The world's recorded production of natural graphite in 1958 totalled about 
200,000 long tons, excluding the output from China and the U.S.S.R., the latter 
country probably producing about 130,000 long tons per annum. Of the world's 

M.c.A.1. — i 225 


recorded production South Korea probably accounted for about 46 per cent., the 
output being mainly the amorphous variety. Next in importance came Austria 
(amorphous), Mexico (amorphous), Federal Germany (crystalline and flake), 
Madagascar (flake and powder), Ceylon (lump, chips and amorphous), Japan, 
Norway (flake), Hong Kong, Italy (amorphous) and the Union of South Africa. No 
graphite is now produced in the United Kingdom, whose imports in 1958 amounted 
to 4,737 long tons of natural graphite and 3,870 long tons of artificial graphite. 
Exports of graphite crucibles totalled 2,392 long tons. The world's largest importers 
of natural graphite are Japan, United States, Federal Germany, United Kingdom, 
Italy, France and Sweden. 

Madagascar has probably the world's largest deposits of flake graphite; these 
occur in a belt of schists and gneisses of considerable extent, having a graphite 
content averaging between 10 and 12 per cent., though some carry up to 60 per cent. 


The most important uses for graphite are for foundry facings and moulds; 
graphite crucibles, ladles, stoppers and nozzles; lubricants, paints, brushes for 
electrical machinery, dry batteries, stove polishes and electrodes. Smaller quantities 
are used in the manufacture of lead pencils, explosives, in electro-typing rubber 
compositions, for preventing scale in boilers, shot polishing, etc. 

Table 78 

U.S. Consumption of Natural Graphite by Uses* 

Short Tons 

































Brake linings 









Carbon brushes 









Crucibles, retorts, 

stoppers and 










Foundry facings . 









Lubricants . 


















Paints and Polishes 









Pencils . 


















Steel making 









Other . 









Total . 









* From U.S. Bur. Mines. 
t Included with Other. 

" Minerals Yearbook," 



The relative amounts of natural graphite consumed for industrial purposes in the 
United States in 1955 and 1958 are shown in Table 78. 

Foundry Facings. The object of foundry facings is to give the surface of the 
moulding sands a smooth skin and to enable the castings to be removed readily on 
cooling. For this purpose, dust grades of either flake, crystalline or amorphous 
graphite are often used. Impurities present in the graphite, unless they have a fairly 
high fusion point, may affect the soundness of the castings. A high-grade graphite is 
not essential for foundry purposes, but some users employ high grade material 
diluted with ground talc, coke or anthracite to reduce cost. On the average, foundry 
facings contain from 40 to 80 per cent, of carbon. 

Crucibles. Although graphite crucibles have been largely superseded in steel 
manufacture, they are still used to a considerable extent in non-ferrous foundry 
work. Flake graphite containing not less than 80 per cent, of carbon is used, the 
material being graded so that it will all pass a 15-mesh sieve and be retained on 
100-mesh. Some crucible makers, however, further refine their flake graphite by 
grinding, and screening off the dust. 

It has been claimed that there is usually no advantage in using a graphite 
containing over 85 per cent, carbon, as a higher percentage often involves a reduction 
in the toughness of the flake. Flake graphite is more suitable for use in crucible 
manufacture than are the acicular or granular types, as it can be orientated to give 
an interlocking structure. 

Mica is one of the most objectionable impurities in crucible graphite, as it often 
fuses readily under the conditions of use and causes pinholes in the crucible. 
Carbonates are objectionable as they decompose on heating and leave shrinkage 
cavities. Sulphur, usually in the form of pyrites, is also undesirable, although it is 
frequently present in small quantities. 

Important features are the uniformity of the graphite, the shape, size and tough- 
ness of the flakes, the burning rate and the packed volume. A low packed volume 
ensures the use of the minimum amount of clay bond and so reduces drying shrink- 
age. As an example of the size grading suitable for crucible manufacture the following 
example of Madagascan graphite may be mentioned: over 20-mesh, 7-8 per cent.; 
between 20- and 35-mesh, 65-7 per cent.; between 30- and 65-mesh, 24-9 per cent.; 
and passing 65-mesh, 1 -6 per cent. 

Specifications for crucible grade graphite in the United States vary considerably, 
but, in general, they require a flake graphite which will all pass a 20-mesh sieve and 
be retained on a 50-mesh, with 75 per cent, passing a 28-mesh and retained on a 
35-mesh sieve. Carbon content varies from 85 to 90 per cent, and the bulk density 
required is such that 100 gm. of the graphite will occupy 129 ml. after repeated 
shaking and jolting. Sulphur in more than traces is objectionable. 

The U.S. National Stockpile Specification P-22a-R, issued on January 14th, 1953, 
for crucible grade graphite, requires the material to have a minimum graphitic 
carbon content of 85 per cent, calculated on the moisture-free basis. It shall be 
sufficiently free from oil and be of such nature with regard to toughness of flakes and 
freedom from thin or ragged edges that it will be capable of meeting, after processing 
in accordance with industrial practice, the specifications placed by crucible manu- 

12 227 


.S. Standard 



20 „ 

30 „ 

40 „ 

50 „ 

60 „ 

facturers upon processed crystalline flake graphite of crucible grade. The material 
must comply with the following specification in regard to size requirements, the test 
being made by agitating 50 gms. for fifteen minutes on a Tyler Ro-Tap sieve shaker. 


99 per cent, passing, min. 
92 „ „ „ max. 

66 „ „ 

25 „ „ 


Lubricants. All types of graphite are extensively used in the preparation of certain 
kinds of lubricants. The graphite, which should be free from grit, is frequently 
deflocculated before use by prolonged agitation with an aqueous solution of tannin 
— 3-6 per cent, of the weight of graphite treated. 

The principal value of the graphite as a lubricant is that it adheres to metal 
surfaces, fills the pores and so reduces the coefficient of friction. For this purpose 
flake variety is usually preferred. Graphite is also used in dry lubricants where oil or 
grease would be objectionable, such as for some textile machinery. 

The U.S. Army Specification (No. 2-64A of 1939) requires that graphite, 
for use either as a dry lubricant, or for compounding with lubricating greases, 
should be a dry powder, free from caking or lumping. The total carbon content 
should be not less than 98 per cent, and the ash should not exceed 1 per cent. The 
graphite should all pass a 100-mesh screen and the residue on 200-mesh should not 
exceed 2 per cent., and when rubbed between two flat polished brass plates, should 
not produce any scratches visible to the naked eye. 

The U.S. Navy Department's Specification 14G5 of September 2, 1941, recog- 
nizes two grades of graphite for use in lubricants: (a) Ash content not exceeding 5 
per cent., graphitic carbon not less than 94 per cent. ; 97 per cent, to pass a 20-mesh 
sieve and 75 per cent, to remain on a 100-mesh sieve; (b) Maximum ash content, 2 per 
cent. ; minimum graphitic carbon, 97 per cent. ; 97 per cent, to pass a 325-mesh sieve. 

U.S. National Stockpile Specification P-22b-R, dated December 16th, 1952, for 
crystalline or flake graphite of lubricant and packing grade, provides for five grades 
of material: A, large flake; B, medium flake; C, small flake; D, fine flake, E, extra 
fine flake. Grades A to D are required to have a minimum content of 95 per cent, of 
graphitic carbon and a maximum for ash plus volatile matter of 5 per cent., each 
calculated on a moisture-free basis. In Grade E a minimum of 96 per cent, graphitic 
carbon and a maximum of 4 per cent, ash plus volatile matter are specified for 
material which has an abrasion loss greater than 4 mg. when tested under conditions 
specified. When the loss is less than 4 mg., the minimum graphitic carbon is 95 per 
cent, and the ash and volatile matter, 5 per cent. 

As regards size, the specification requires that the material shall conform to the 
requirements shown in Table 79 when a representative sample of 100 gm. is agitated 
for the periods shown. 



Table 79 

Graphite — Lubricant and Packing Grade. 
U.S. National Stockpile Specification P-22b-R 

Grade and Period of Agitation 

Passing U.S. 
Standard Sieve 

Per cent by weight 


Large flake (15 min.) .... 





minimum 95 
maximum 40 



Medium flake (15 min.) 



minimum 95 
maximum 15 


Small flake (15 min.) .... 



minimum 70 
maximum 30 


Fine flake (30 min.) .... 


minimum 98 
maximum 95 


Extra fine flake (45 min.) 



minimum 99-5 

Aircraft Material Specification D.T.D. 77 issued by the U.K. Ministry of Supply, 
requires powdered graphite to contain not less than 57 per cent, carbon. The 
material must all pass a 200-mesh I.M.M. sieve and contain not over 1 -25 per cent, 
moisture (at 700° C.) nor more than 1 -25 per cent, water-soluble matter. The 
quantity extracted by petroleum-ether must not exceed 0-5 per cent, and the water- 
extract must not have an acid reaction. 

Paint. The properties of graphite which make it valuable as a constituent of 
anti-corrosive paint are a grey metallic colour, great opacity, low specific gravity, 
and the shape and water-repellant character of its particles when ground. It is also 
resistant to heat, most acids and chlorine, and when incorporated in paint adheres 
well to iron and steel. 

Opinions in the trade differ regarding the suitability of high-grade graphite as 
the sole pigment in anti-corrosive paints, as some varieties tend to flocculate in oil 
media and to spread under the brush into a very thin coating. An impure variety 
known commercially as silico-graphite is, however, extensively used. Such a material 
produced in Ceylon has the following percentage composition: carbon, 54-7; silica, 
24-4; alumina, 12; ferric oxide, 3-9; lime, 1-2; magnesia, 11. It is claimed that a 
graphite containing only 25 per cent, of graphitic carbon, and produced in Michigan, 
U.S.A., gives a satisfactory pigment when ground. Some paint manufacturers use a 
high-grade graphite diluted with silica to reduce cost and to improve its physical 
properties as a pigment. 

Graphite for use in paint should be free from pyrite (which is liable to oxidize on 
exposure to air) and mica. Possibly about 5 per cent, of the total production of 
graphite is utilized by the paint industry. 

Processed Graphite {Brushes, etc.). Many grades of brushes for dynamo and 
motor commutators contain fine crystalline graphite. Grades for use at high current 
densities have copper powder as an additional constituent. Brushes capable of 
running cool at high speeds, of successfully resisting mechanical shocks and of 



carrying very heavy overloads have no natural graphite in their composition. They 
are made from various types of amorphous carbon and the final process in manu- 
facture is the conversion of the carbon into artificial graphite by subjecting the 
material to very high temperature in an electric furnace. 

Boiler Compounds. Finely ground graphite is sometimes used to prevent the 
formation of, or to break up, scale in boilers. Its action is stated to be mechanical 
and not affected by the acidity or alkalinity of the feed water. For this purpose flake 
graphite is usually recommended but the amorphous variety is sometimes used. 

Explosives. Graphite is used in the manufacture of certain types of smokeless 
and other powders. The specifications for the purchase of graphite for these purposes, 
as laid down by one of the largest users in Great Britain, are summarized in Table 
80. All samples are required to be free from sand and grit. 

Table 80 

Graphite for Use in Explosives 










100° C. 


extract * 
(as H s S0 4 ) 

Per cent. 

Per cent. 

Per cent. 

Per cent. 

Black powder. 

All through 100-mesh 





Propellant explosives 

All through 100-mesh 






Negro powder t 

85 per cent, through 

80-mesh I.M.M. 





* Calculated on the original material. 

t The colouring power of the graphite, as estimated by grinding 1 per cent, of the 
sample with 99 per cent, of ammonium nitrate, must not be less than that given by a 
standard sample of graphite provided by the purchasers. 

Dry Cell and Battery Manufacture. Graphite is used in the manufacture of dry 
cells and batteries to give conductivity to the mass of manganese dioxide. Flake 
graphite is often preferred for this purpose, but a certain quantity of both crystalline 
and amorphous types is used. 

The graphite should not contain metallic impurities which are soluble in a battery 
electrolyte composed of 15 per cent, each of ammonium chloride and zinc chloride, 
as such impurities will plate out on to the zinc in the cell. The resistance of flake 
graphite is about 080 ohms per cu. in. but that of artificial graphite is much lower, 
often about 0-025 ohms. 

Some users specify a minimum carbon content of 85 per cent, with the following 
maximum percentage limits for certain impurities: iron, 2-5; copper, 003; nickel 
and cobalt, 03 ; arsenic and antimony, 03. The material is usually ground so that 
at least 85 per cent, will pass a 200-mesh sieve. 

Very finely divided (micronized) graphite is used in the mercuric oxide Ruben 
battery and for this purpose a high purity material is required containing about 97 
per cent, of carbon and fairly free from lead, copper, sulphur and nitrates. The limit 



for copper is about 005 per cent. Natural graphite is preferred to artificial as it 
bonds better with the mercuric oxide. 

The U.S. National Stockpile Specification P-21-R, issued on January 14th, 1953, 
for amorphous lump graphite, requires the product to have a minimum graphitic 
carbon content of 97 per cent., calculated on a moisture-free basis. The lumps should 
have a greasy feel; a lustrous conchoidal fracture; must not contain the tough 
needle and flaky crystalline formations which are characteristic of crucible grade 
graphite, and the material must not be hard, or dull and cokey in appearance. No 
lumps may be over 5 in. in diameter and at least 90 per cent, must be retained on a 
No. 10 U.S. Standard sieve and 97 per cent, on a No. 6 sieve. 

Stove Polish. Amorphous graphite, such as that produced in Korea, Hong Kong 
and Mexico, is usually employed for this purpose, but occasionally the crystalline 
variety is used. A carbon content of about 80 per cent, is preferred. The graphite, 
which should be of a dark black colour and capable of taking a good polish, may be 
bonded with clay, rosin and soap to produce a coherent block. 

Pencils. The so-called lead of pencils consists of a mixture of soft amorphous 
graphite, clay and antimony sulphide which have been baked at a temperature 
between 1,815 and 1,093° C. Only a few graphites possess the necessary depth of 
colour, softness and purity. 

Bavarian, Bohemian, Mexican and Siberian graphites are preferred for this 
purpose but blends of Ceylon and amorphous graphite have proved satisfactory. 
Flake graphite is not usually accepted for pencil manufacture as the material, even 
after very fine grinding, still preserves its flaky character. The Mexican graphite 
used for pencils is stated to approximate to the following percentage composition: 
carbon, 86; silica, 7; iron oxide, 0-5-1 ; alumina, 5. 

Thermocouples. Silicon carbide/graphite thermocouples have been developed by 
the Morgan Crucible Company of London. They consist of an inner graphite rod 
cemented to an outer silicon carbide tube and it is claimed that it should be possible 
to use them for temperatures up to about 1,900° C. without a protective sheath. 
Voltages of the order of 250-500 millivolts are obtained in the range 1,000-1,900° C. 

Carbon in Plant. In recent years carbon in various forms has found increasing 
use in certain types of plant where conventional materials are unsuitable, either by 
reason of their chemical reactivity or need for lubrication. Thus, according to 
Lyddon and Hurden, carbon bearings are used in pressure vessels and mixers 
where they may come into contact with chemical solutions, in rotary mechanical 
seals in several types of pump, and for piston rings in oil-free reciprocating gas 
compressors. Several modes of preparation can be used, varying with the demands 
likely to be made on the final product. The raw materials, which are various forms 
of carbon or graphite, are reduced to fine powder, mixed with suitable binders and 
pressed into blank shapes or extruded as tubes or rods. The ware so produced is first 
heated to drive off the volatile matter in the binder and then carbonized so as to 
produce a hard, homogeneous material suitable for machining. The so-called 
" plain carbon " grades are produced by this single carbonization, but if a graphitic 
carbon product is required, a further heat treatment in an electric furnace at about 
2,500° C. is given. 



A group of carbon products, known as " Delanium," are of importance in some 
types of chemical plant. Delanium products are made by the controlled carboniza- 
tion of bituminous coal under conditions which result in the formation of a 
considerable proportion of /}-carbon, a product characterized by its hardness, 
high compressive and tensile strength and optical reflectivity. Delanium carbon 
can be converted to graphite by heating in an electric furnace to about 3,000° C. 
Delanium carbon tiles are used in chemical industry for lining tanks, reaction 
vessels, scrubbing towers and other types of plant where corrosive liquids have to 
be dealt with. A useful summary of the production, properties and uses of Delanium 
carbon has been given by W. S. Norman, Z. A. Hilliard and C. H. V. Sawyer 

Artificial Graphite 

Artificial graphite is the name given to graphite formed from coke or other 
forms of amorphous carbon by the process of " graphitization," which involves 
the heat treatment of the amorphous carbon in inert atmospheres to temperatures 
between 2,000 and 3,000° C. 

The world's annual production of artificial graphite probably amounts to 
several hundred thousand tons, most of the output being used as electrodes or 

The standard commercial method for making artificial graphite is still basically 
the same as that of the Acheson process devized about 1 896. In this method petroleum 
coke, or coke from coal or pitch, is ground, sized, mixed with a suitable binder, 
shaped into blocks, tubes or rods and then heated in a non-oxidizing atmosphere in 
a gas furnace at temperatures varying between 900 and 1,300° C, depending upon 
the use for which the carbon is intended. The mass is next graphitized by passing 
an electric current through it and so raising its temperature to not less than 2,500° C. 
The process of graphitizing causes some molecular rearrangements, decomposition 
of residual hydrocarbons, removal by distillation of many impurities and a crystal 
growth in which the carbon atoms are re-arranged in a lattice that corresponds 
closely with that of natural graphite. Artificial graphite, while never so unctuous and 
highly crystalline as the natural product, has most of its physical properties. It is 
usually much purer than the natural product and it is quite possible to produce it of 
99-99 per cent, carbon content. Petroleum coke is stated to be the most suitable 
starting material for making high quality artificial graphite. Pitch coke is not so 
suitable, but is well adapted for making certain varieties of amorphous carbon 
aggregate. The density of graphite single crystal is 2-26 gm./cc, that of natural 
graphite varies between 2-0 and 2-25 gm./cc., whilst that of artificial graphite 
ranges between 1 -5 and 1 -8 gm./cc. Since the quantity of electrical energy required 
to produce artificial graphite is considerable, the cost is much higher than that of 
natural graphite. 

Artificial graphite is the most extensively used moderator in nuclear reactors. 
The purpose of a moderator, according to E. E. Lockett, is to slow down the high 
energy neutrons released in fission. This slowing down, or " moderation," is achieved 
by elastic collision between the neutrons and the nuclei of the moderator, each 



collision resulting in the transfer of some of the nuclear energy to the moderator 
atom struck. The neutrons produced in fission have an energy spectrum extending to 
15 million electron volts (Mev.) or more, with a mean energy of about 2 Mev, and 
the ratio of moderator to fissile atoms in the reactor will determine the extent to 
which this spectrum is degraded. A reactor, where sufficient moderator is present 
to reduce the energy of the neutrons until most of them are in thermal equilibrium 
with the moderator, is said to be a " thermal reactor " and the low-energy neutrons 
are known as thermal neutrons. These thermal neutrons will diffuse in the reactor 
until they are captured, or escape from the surfaces, and they will have normal 
Maxwellian distribution of energies corresponding to the temperature of the system. 
For a temperature of 20° C. the mean energy of the thermal neutrons is about l/40th 
of an electron volt. 

According to A. B. Mcintosh and his co-workers normal reactor graphite has a 
bulk density in the range of 1 -7-1 -8 g./c.c. The theoretical X-ray density of graphite 
derived from perfect graphite lattice is 2-26 g./cc. and considerable differences exist 
between the properties of the ideal high density graphite and the pile graphite 
produced commercially. With reactors of the Calder Hall type, the principal mech- 
anical requirement is compressive strength adequate to allow the graphite to support 
the weight of the graphite structure above. Among physical properties, the density, 
the coefficient of thermal conductivity, porosity, and also that of thermal expansion 
are relevant. 

Artificial graphite for nuclear purposes is made in Great Britain by the Anglo- 
Great Lakes Corporation Ltd. at Newcastle upon Tyne. 

The use of manufactured graphite as a high temperature material in missiles and 
rockets has been described by J. E. Hove (1958). 


" Structure of Graphite in Relation to Crucible Making." By R. Thiessen. J. Amer. Ceram. Soc. 

" Graphite." By H. S. Spence. Canad. Dept. Mines, Bull No. 511, 1920, 202 pp. + 56 plates and 

" Industrial Carbon." By C. L. Mantell. New York, 1928, 410 pp. 
" Marketing Graphite." By P. M. Tyler and C. H. Harness. U.S. Bur. Mines, Inform. Ctrc. No. 

7177, 1941, 12 pp. 
" Graphite in Paints." By C. L. Mantell. " Protective and Decorative Coatings." Ed. J. J. 

Mattiello, Lond., 1942, Vol. 2, pp. 548-54. 
" Graphite as a Paint Pigment." By C. R. Draper. Paint Manuf., 1942, 11, 20-6 and 55-7, includ- 
ing bibliography. 
" Graphite, Natural and Manufactured." By G. R. Gwinn. U.S. Bur. Mines, Inform. Clrc. 

No. 7266, 1943, 26 pp., including bibliography. 
" Graphite." Anon. Min. Res. Australia, Sum. Rep. No. 5. Canberra, 1946, 29 pp. 
" Carbon and Graphite for the Engineer." By C. L. Bodran Griffith. Industr. Chem., 1948, 24, 

" Graphite for the Manufacture of Crucibles." By G. R. Gwinn. Amer. Inst. Min. Met. Eng.; 

Mln. Tech., T.P. No. 1909, 4 pp. 
" Primary Batteries." By G. W. Vinal. Lond., 1950, 336 pp. (Graphite, pp. 73-6.) 
" Delanium Carbon in Chemical Plant Construction." By W. S. Norman, A. Hilliard and 

C. H. V. Sawyer in " Materials of Construction in the Chemical Industry." Society of 

Chemical Industry, Lond., 1950, pp. 269-273. 
" Non-Metallic Minerals." By R. B. Ladoo and W. M. Myers. New York, 1951. (Graphite, 

pp. 250-8, including bibliography.) 
" Baked Carbon and Graphite Products." By H. W. Abbott. " Encyclo. of Chem. Tech." Ed. by 

R. E. Kirk and D. F. Othmer. New York, Vol. 3, pp. 1-34. 
" Natural Graphite." By B. B. Seeley and E. Einendorfer, ibid., pp. 84-104. 
" Structural and Graphitized Carbon." By F. J. Vosburgh, ibid., pp. 104-112. 



" Materials for Nuclear Power Reactors." By J. M. Warde. Materials and Methods, 1956, 44. 

No. 2, 121^4. 
" Graphite." By F. D. Lamb and D. R. Irving. " Mineral Facts and Problems," U.S. Bur. Mines, 

Bull. 556, 1956, pp. 327-37. 
" The Production and Properties of Graphite for Reactors." By L. M. Currie, V. C. Hamister and 

H. G. McPherson. National Carbon Div., Union Carbide and Carbon Corp., New York, 

1956, 61 pp. 
" Proceedings of the 1st and 2nd Conferences on Carbon." University of Buffalo, N.Y., 1956. 

212 pp. 
" The Purification of Graphite; bibliography 1926-1955." By P. M. Harris. U.K. Atomic Energy 

Research Est. Inform Bull. 109, 1957, 7 pp. 
" Review of Radiation Damage to Graphite." By G. R. Hennig. Progress in Nuclear Energy 

Series V, Metallurgy and Fuels, Vol. I, Ed. by H. M. Finniston and J. P. Howe. Lond.. 1956. 

pp. 587-651. 
" The Nature of Artificial Carbons." By S. Mrozowski. " Industrial Carbon and Graphite." 

(Papers read at the Conference held in London, 24th-26th Sept., 1957.) Society of Chemical 

Industry, Lond., 1958, pp. 7-18. 
" The Harwell Experimental Graphite Plant." By M. S. T. Price and F. W. Yeats, ibid.,\ll-l24. 
" The Use of Graphite as a Moderator in Nuclear Reactors." By E. E. Lockett, ibid., 493-500. 
" Physical and Mechanical Properties of Graphite Moderators." By A. B. Mcintosh, T. J. Heal 

and A. Cowan, ibid., 560-64. 
" Porous Structure and Absorption Properties of Active Carbons." By M. M. Dubinin, ibid.. 

" Problemes poses par la Fabrication du Graphite nucleaire." By P. Cornuault and H. des 

Rochettes, ibid., 527-37. 
" Some Mechanical Engineering Applications of Carbon." By P. E. Lyddon, and R. K. Hurden, 

ibid., 579-584. 
" Tars and Pitches as Binders for Carbon and Graphite." By T. H. Blakeley and F. K. Earp 

ibid., 173-7. 
" Graphite as a High Temperature Material." By J. E. Hove. Trans. Metallur. Soc. A.I.M.E.. 

1958, 212, (Feb.), 7-13. 
" Graphite and its Crystal Compounds." By A. R. J. P. Ubbelohde. London, 1959, 250 pp. 
" Nuclear Graphite Production." Nuclear Engineering, 1959, April, 4 pp. 
" Graphite." By E. N. Cameron. " Industrial Minerals and Rocks." Amer. Inst. Min. Met. 

Petrol. Eng., 1960, 3rd Ed., pp. 455^169. 
"Graphite." U.S. Bur. Mines. Minerals Yearbook. (Annual). 

Standard Specifications 

U.K. Ministry of Supply, Aircraft Material Specification 

Powdered Graphite. D.T.D. 77. 
U.S. Army Specification 

Graphite for use as a lubricant, etc., No. 2-64A, 1939. 
U.S. Navy Specification 

Graphite, No. 14G5, Sept. 2nd, 1941. 
U.S. National Stockpile Specifications 

Amorphous Lump Graphite. P-21-R, Jan. 14th, 1953. 

Crystalline Flake Graphite, Crucible Grade. P-22a-R, Jan. 14th, 1953. 

Crystalline and Flake Graphite, lubricant and packing grade. P-22b-R, Dec. 16th, 1952. 


The mineral known as greensand or glauconite is a complex hydrated silicate of 
ferroso-ferric iron and potassium which usually contains some magnesium and 
aluminium and approximates to the formula K . Mg(Fe . Al)Si02,3H 2 0. It therefore 
has the same chemical composition as celadonite (see p. 443), but whereas the latter 
mineral usually originates in vesicular basalt, glauconite is of sedimentary origin. 

Glauconite is of somewhat variable composition and hence its specific gravity 
varies between about 2-2 and 2-8, its refractive index may be between 1 -59 and 1 -64 



and its hardness ranges from 2 to 3. The content of potash (K2O) varies between 4 
and 8 per cent. It is usually found as rounded or subangular granules which appear 
blackish-green by reflected light. 

World Production 

Although small quantities of greensand and glauconite are worked in some 
countries, statistics are available only for the United States, whose output of 
marketable greensand has ranged between about 2,000 and 6,000 long tons per 
annum in recent years, and Australia, where in 1958, 112 long tons of glauconite 
were produced from 560 long tons of greensand. All the Australian production 
comes from Gin Gin, Western Australia, the treated glauconite being largely 
exported to Europe under the name " Mollinite." 

Practically the whole U.S. output came from Burlington and Gloucester 
Counties, New Jersey and Calvert County, Md. Of the greensand sold, about 
70 per cent, was used as a soil conditioner, and the remainder in water softeners. 
Large supplies of greensand are available, if required, in the Bracklesham Beds 
formation of the London Basin of England. 


At the present time the chief use is as a base-exchange water softener, but small 
quantities are sometimes used in the preparation of pigments. In countries where 
large supplies are available, particularly in England, France, Belgium, United States 
and Western Australia, greensands containing large percentages of glauconite have 
been used for generations in hopyards, orchards and market gardens as a slow- 
acting potash manure. Its use however, decreased rapidly when more concentrated 
and rapidly acting potash fertilizers became available from Germany, France and 
elsewhere, and greensand is now only used as a fertilizer where large supplies are 
available at cheap rates. 

At various times attempts have been made to utilize greensand on a commercial 
scale as a source of potash salts. Thus, one process, formerly used in the United 
States, consisted in heating the material with lime slowly at 200°C. and recovering 
caustic potash by leaching. 

Water-softeners. Greensand as mined, before being used for water softening, is 
usually concentrated so as to separate the glauconite from other minerals, such as 
quartz, calcite, and clay. Concentration may be effected by gravity methods using a 
strong caustic soda solution. The separated glauconite is generally activated by 
chemical means in order to improve its base exchange properties. The chemicals 
employed have included brine, sodium silicate and magnesium fluosilicate. 

Both untreated and activated glauconite are rather liable to disintegrate alter 
being subjected to repeated regeneration with brine, and various methods have been 
used to make their surfaces more resistant. One of these is to heat the material for 
some time at 700° C, but, according to some observers, this treatment reduces the 
base-exchange value of the material. Chemical means of hardening the surface have 
also been used, such as treatment with solutions of sodium silicate. 

In the past, treated glauconite concentrates from greensand have been extensively 



used in water-softening plants in Great Britain, particularly at large industrial 
plants, the material in most cases being imported from New Jersey, U.S.A. or 
Western Australia. In recent years, however, glauconite has been replaced for this 
purpose by synthetic zeolites, carbonaceous zeolites, and by artificial base-exchange 
resins, which are more effective weight for weight. It would appear that glauconite 
is now only produced to supply the needs of out-of-date water softening plant. 

Table 81 gives some useful data concerning the relative base exchange capacities 
of some glauconites and synthetic zeolites which have been quoted by K. P. Oakley 
in Wartime Pamphlet No. 33, published in 1943 by the Geological Survey of Great 

Table 81 

Average Base-Exchange Capacities of Glauconites and Other Water-softening Materials 



lents per 


100 gm. 

per cu. ft. 

Knaphill glauconite (untreated) 






W. Australian glauconite (treated) 



New Jersey „ „ . . 



Nutfield fullers' earth (granular, treated) 



Carbonaceous " zeolite " (treated coal) . 



Synthetic zeolite 



Neither natural nor treated glauconite is suitable for softening waters which 
contain much oily or suspended matter, as these may be deposited on the surface of 
the mineral and so impair its utility. Waters containing iron may also deposit ferric 
hydroxide on the surface or may cause the substitution of iron for sodium in the 
glauconite, a reaction which is not reversible under the conditions normally used for 
regenerating glauconite. Slightly acid waters may also cause trouble by accelerating 

Table 82 

Properties of Some Treated Glauconites from New Jersey, U.S.A. 



HI-Basex A 







Porosity, per cent 




Screen analysis ..... 




Exchange capacity in grains CaCO s per 

cu. ft 




Temperature of raw water, max. 

105° F. 

100° F. 

100° F. 

Turbidity of raw water, max. . 

10 ppm. 

5-7 ppm. 

5 ppm. 

Iron in raw water, max. .... 

2-5 ppm. 

1-5 ppm. 

1 ppm. 

Attrition loss per cent, per annum 




Recommended pH operating range . 




Recommended maximum softening rate, 

per sq. ft. bed area .... 

5 g.p.m. 

5 g.p.m. 

5 g.p.m. 



the disintegration of the mineral. In view of the above, it is customary for firms who 
market treated glauconite so specify limits for the above impurities in waters to be 
treated. Limits recommended by the Inversand Co., of Clayton, New Jersey, 
U.S.A., for some of their treated glauconites are shown in Table 82. 

A manganese zeolite, known as " Ferrosand," made from glauconite, is produced 
and marketed by the Inversand Co., of New Jersey, U.S.A., and used to remove 
soluble iron or manganese salts from well waters, up to a maximum of about 15 

Pigment Manufacture. On account of its greenish colour, ground glauconite has 
been suggested for use as a pigment, but it is not particularly suitable for this 
purpose owing to its low refractive index and the comparative ease with which it 
weathers to a rusty coloured limonitic product. It can be used, however, in place of 
" green earth " or celadonite as an adsorbent or fixing base for aniline colours and 
for making green pigments for use in distempers by impregnating it with up to 5 per 
cent, of malachite green. 


" Potash in the Greensands of New Jersey." By G. R. Mansfield. U.S. Geol. Surv., Bull. 727, 1922, 

46 pp. 
" Water Softening: The Base Exchange or Zeolite Process, Summary of Existing Knowledge." 

By A. R. Martin. Dept. Sci. Industr. Res., Water Pollution Res., Tech. Paper No. 1, 1929, 

20 pp., including bibliography. 
" Glauconite Deposits at Gin Gin." By F. R. Feldtman. Ann. Rep., Geol. Surv. W. Australia, 

1933, pp. 6-8. 
" Glauconite, Its Distribution and Uses." By E. S. Simpson. Chem. Eng. Min. Rev., 1934, 26, 

" The Preparation of Base Exchange Materials from Some British Clays and Minerals." By H. 

Ingleson and W. H. Sullivan. /. Soc. Chem. Ind., 1941, 60, 11-15. 
" Glauconite Sand of Bracklesham Beds, London Basin." By K. P. Oakley. Geol. Surv.: England 

and Wales, Wartime Pamphlet No. 33, 1943, 28 pp. fcp., including bibliography. 
" The Maintenance of Zeolite Filters." By P. Boynton and H. Gay. /. Amer. Waterworks Assoc, 

1949, 41, 187-8. 
" Minor Non-metals." U.S. Bur. Mines, Minerals Yearbook (Annual). 

Gypsum and Anhydrite 

Gypsum is a natural hydrated sulphate of calcium (CaSC>4 . 2H2O), whilst anhydrite, 
as its name implies, is the sulphate without water of crystallization. Gypsum when 
pure contains SO3, 46-5 per cent., CaO, 32-6 per cent., and water 20-9 per cent. It 
has a specific gravity of 2-35, hardness between 1 -5 and 2-5, and a refractive index of 

Gypsum commonly occurs massive but special forms are known, e.g. a clear 
crystalline variety known as selenite, a massive granular form known as alabaster 
and a fibrous type called satin spar. 

Anhydrite, which has a specific gravity of 2.95, a hardness of 3-3-5, and a re- 
fractive index of 1-59, is finding increasing use in conjunction with synthetic 



ammonia in the manufacture of ammonium sulphate, for sulphuric acid production 
and in special plasters. It can also partly replace gypsum as a retarder in Portland 
cement and as an extender in certain paints. 

Artificial anhydrite, or anhydrous calcium sulphate, is extensively employed as a 
filler in such articles as rubber soles and heels. Its principal use, however, is in the 
manufacture of the anhydrous types of wall plaster. 

World Production 

The world's annual recorded production of gypsum amounts to about 32 million 
long tons, but this total excludes gypsum known to have been produced in Bulgaria, 
Roumania, Cuba, Mexico, China, Korea and many other countries. The largest 
recorded outputs of gypsum in order of magnitude are obtained in the United 
States, Canada, France, the United Kingdom, the U.S.S.R., Spain, India, Federal 
Germany, Italy, Austria, Jamaica, Australia and Japan (all over 450,000 long tons 
per annum). Great Britain in 1958 produced 1,486,800 long tons of gypsum and 
1,764,400 long tons of anhydrite. Imports comprised 78,544 long tons of crude 
gypsum and alabaster and 842 long tons of calcined gypsum. The world's largest 
importer of crude gypsum is the United States, which in 1958 took 3,614,942 long 
tons. The largest exporter of gypsum is Canada, with 2,587,705 long tons in 1958. 

A comprehensive account of world occurrencies of gypsum and anhydrite and 
the preparation and uses of products derived therefrom will be found in " Gypsum 
and Anhydrite " by Dr. A. W. Groves. 


Gypsum is used principally for making plaster of Paris and special hard finish 
plasters, such as Keene's and Parian, and for controlling the setting time of Portland 
cement. Anhydrite is used mainly in the manufacture of sulphuric acid and 
ammonium sulphate and as a source of elemental sulphur. 

Ground gypsum is used in the paint industry under the names of " mineral 
white " or " terra alba," and as a filler for paper and in finishing cotton goods. 
Relatively minor uses for gypsum include increasing the permanent hardness of the 
water used in brewing. 

A certain amount of low-quality gypsum is ground and used as a fertilizer (under 
the name of " land plaster ") and for polishing tin plate. 

Alabaster, the massive granular variety of gypsum, is well-known as an orna- 
mental stone in statuary, interior decoration and ornaments. 

A useful indication of the relative amounts of gypsum consumed by various 
industries is afforded by Table 83 relating to the United States. 

Plaster of Paris. When gypsum is heated to a temperature of about 130° C, it 
loses a proportion of its water of crystallization and forms the quick-setting cement 
known as plaster of Paris, which is extensively used in the manufacture of plaster- 
board for building purposes, in moulds for modelling, and in the marble-working 
and lithographic industries. Very pure high-grade plaster is also used in dentistry and 
orthopaedic surgery. 



Table 83 

Gypsum Products Consumption in the United States, by Uses.* 

Short Tons 




Portland cement retarder 
Agricultural gypsum .... 
Other usesf 










Total, Uncalcined ..... 





Plate glass and terracotta plasters 

Pottery plasters 

Orthopaedic and dental plasters 

Industrial moulding, art and casting 

Other industrial usesj .... 









Total, Industrial ..... 






Prefabricated || 




Total, Building 




* Adapted from " Minerals Yearbook," U.S. Bur. Mines. 

t Includes uncalcined gypsum used as filler and rock dust, in brewers' fixe, in colour 
manufacture and for unspecified uses. 

} Includes dead-burned filler, granite polishing and miscellaneous uses. 
II Includes weight of paper, metal or other materials. 
§ Excludes Tile. 

The so-called calcination of gypsum for the preparation of plaster of Paris is 
usually carried out in either a " kettle " or in a rotary kiln. If the rotary kiln process 
is to be used the raw gypsum is crushed to pass a lj-in screen, but for the kettle 
process finer grinding is required. 

The kettles are cylindrical steel shells which have a diameter from 8-15 ft. and a 
depth of 6-14 ft. The kettles are heated by horizontal flues of 8-14 in. in diameter, 
usually four flues arranged in pairs. To prevent local overheating, the gypsum is 
constantly agitated by horizontal rabble arms which are attached to a vertical gear- 
driven shaft, arrangements being provided for loading the kettle from the top and 
for discharging the finished product from the bottom. 

When the temperature of the mass reaches about 120°C, the gypsum appears 
to boil, owing to the emission of water vapour due to the release of the water of 
crystallization from the mineral. The temperature is gradually increased to about 
150°C. until the boiling ceases, indicating that most of the gypsum has been con- 
verted into the hemi-hydrate. Heating is continued until 170°C. is reached and 
action has apparently ceased, when the material is discharged into the hot-pit and is 



known as " first settle " calcined gypsum and contains about 5-6 per cent, of water. 
The whole operation of calcining occupies from one to three hours. 

First settle gypsum is the material commonly used for making gypsum board and 
wall plaster and for most of the ordinary uses of plaster of Paris. It is usually neces- 
sary, however, to treat the gypsum with some substance, such as glue, in order to 
retard its setting time. 

For some special purposes, a more highly calcined product is required, having 
less plasticity but greater density and strength than first settle gypsum. This product 
can be obtained either by continuing the heating in the kettle up to 380° C, whereby 
the content of water is reduced to 1 -5 per cent., or more generally by so-called 
" ageing " methods. These latter may consist of exposing the first settle gypsum to 
air for some time, or by adding a chemical, such as calcium chloride, to the raw 
gypsum before calcination. These specially aged plasters are employed where it is 
desirable to use the minimum quantity of water for mixing and have few voids in the 
finished product, such as in plaster casts, moulding and for dental and orthopaedic 

Rotary calciners used for gypsum much resemble those used for Portland cement 
and range in length from 70-150 ft., and in diameter from 6-8 ft. They have outside 
combustion chambers and counterflow firing. Gypsum, previously crushed to pass 
1 J-mesh, takes about forty-five minutes to pass through the kiln, the temperature of 
which ranges between 160 and 190° C. The product on leaving the kiln passes 
directly to the regrinding mills, where the " calcination " of the larger fragments is 
completed. It is claimed that tube grinding increases the bulk, plasticity and sand- 
carrying capacity of the plaster. 

The product obtained from the rotary kiln is stated to be more suitable for use in 
wall plasters where extreme exactness of setting time is not required, or can be 
controlled during mixing, or when the plaster is intended to be used for the manu- 
facture of block or board. The rotary kiln product is stated to be not so suitable as 
the kettle calcined plaster for use in the ceramic industry owing to its lack of 
uniformity. It is stated that a microscopic examination shows the rotary product 
often to be a mechanical mixture of uncalcined gypsum associated with material in 
varying degrees of calcination. So far as is known, only one rotary calciner is in use 
in Great Britain for treating gypsum. 

British Standard Specification B.S. 1191 : 1955 requires that gypsum plaster for 
building purposes shall be one of the following classes: (A) plaster of Paris; (B) 
retarded hemi-hydrate gypsum plaster; (C) anhydrous gypsum-plaster; (D) Keenes 
or Parian. As regards purity, no materials shall be added to gypsum plaster, except 
such as are necessary to control the setting and working characteristics, or to impart 
anti-corrosion or fungicidal properties. 

The chemical composition of class (A) plaster of Paris shall be such that its sulphur 
trioxide content, expressed as a percentage by weight of the plaster as received shall 
not be less than 35 ; the calcium oxide content shall not be less than two-thirds of the 
sulphur trioxide content; the soluble sodium and magnesium salts content, expressed 
as percentages of sodium oxide (Na20) and magnesium oxide (MgO) by weight of 
the plaster as received shall each be not greater than 01. The loss on ignition shall 



not be greater than 9 per cent, or less than 4 per cent, by weight of the plaster as 
received. The residue on a B.S. No. 14 sieve shall not be greater than 5 per cent, by 
weight. Set plaster pats shall show no signs of disintegration, popping or pitting when 
examined by the prescribed method. The transverse strength (modulus of rupture) 
of the set plaster shall be not less than 170 lb./in. 2 (1 1 -9 kg./cm. 2 ) when determined 
by the prescribed method. 

Class (B) retarded hemi-hydrate gypsum plaster may be one of the following 
types: (a) undercoat plaster, (b) finishing plaster, (c) dual purpose plaster (undercoat 
and finishing). The chemical composition shall be the same as for class (A) plaster of 
Paris above. The residue on a B.S. No. 14 sieve shall not be greater than one per cent, 
by weight and the transverse strength (modulus of rupture) of the set sanded plaster 
shall not be less than 200 lb./sq. in. (14 kg./cm. 2 ). Set plaster pats shall show no 
signs of disintegration, popping or pitting when examined by the prescribed 

In classes (A) and (B) where specially low expansion on setting is required, 
provision for this property shall be made by agreement between purchaser and 
manufacturer. With material in class (B), when plaster of low setting expansion is 
required, under the above standard specification the linear expansion on setting 
shall not exceed 0-20 per cent, in one day when tested in accordance with the pre- 
scribed method. 

Class (C) — anhydrous gypsum plaster shall be one of the following types: (a) 
undercoat plaster; (b) finishing plaster; (c) dual purpose plaster (undercoat and 
finishing). As regards chemical composition, the sulphur trioxide content, expressed 
as a percentage of the plaster as received, shall not be less than 40 ; the calcium oxide 
content shall not be less than two-thirds of the sulphur trioxide content by weight; 
the soluble sodium and magnesium salts content, expressed as percentages of sodium 
oxide (Na20) and magnesium oxide (MgO) shall not be greater than 01 per cent, of 
the weight of the plaster as received; the loss on ignition shall not exceed 3 per cent, 
by weight. The residue on a B.S. No. 14 sieve shall not exceed 1 per cent, by weight. 
The requirement for soundness is that the set plaster pats shall show no signs of 
disintegration, popping or pitting when examined by the prescribed method. Tests 
are also provided for transverse strength of the set sanded plaster with admixture of 
lime and for the mechanical resistance of the set neat plaster. 

Class (D) Keenes or Parian gypsum plaster — this is a plaster of the anhydrous 
type characterized by being easily brought to a smooth and clean finish, associated 
with a slow and gradual set. The special qualities traditionally associated with 
Keenes or Parian cannot be dealt with at present by any convenient direct tests. In 
the British Standard Specification, Keenes or Parian shall be differentiated from other 
gypsum plaster of the anhydrous type (class (Q) by a higher standard of purity and 
hardness and by specifying a limit of expansion on setting. The chemical composition 
shall comply with the following requirements : Each of the three types shall contain 
not less than 47 per cent, of SO3 (calculated on the material as received) and the 
percentage of CaO shall be not less than two-thirds of that of SO3. The loss on ignition 
is limited to 2 per cent, and the material not passing a No. 14 B.S. sieve must not 
exceed 1 per cent. Tests are also specified for soundness for all three types and, in the 



case of finishing and dual purpose cement, also for transverse strength and mechani- 
cal resistance. The expansion on setting for any of the types must not exceed 0-5 
per cent, at four days after gauging. 

Gypsum concrete is dealt with in A.S.T.M. specification C 317-55, which covers 
mill-mixed gypsum concrete, consisting essentially of calcined gypsum and suitable 
aggregate, requiring the addition of water only at the job. Gypsum concrete is 
intended for use in the construction of poured-in-place roof decks or slabs. Two 
classes, based on compressive strength and density, are covered. Gypsum concrete 
shall consist essentially of calcined gypsum and wood chips or wood shavings, 
proportioned to meet the applicable requirements of this specification. Calcined 
gypsum shall conform to the requirements of A.S.T.M. Specification C 28 for 
gypsum plasters. Wood chips or wood shavings shall be of dry wood, uniform in 
appearance and clean, shall pass a 1-inch sieve and shall be not more than jg in. 
thickness. Gypsum concrete shall have a setting time of not less than twenty or 
more than ninety minutes. It shall have compressive strength as follows: 

Class A 500 p.s.i. min. 
Class B 1,000 p.s.i. min. 

Class (A) gypsum concrete shall have a density of not more than 60 lb. per cu. ft. 
A.S.T.M. Specification C 28-58 for gypsum plasters covers five types, namely, 
ready-mixed plaster, neat plaster, wood-fibred plaster, gypsum bond plaster, and 
gauging plaster for finishing coat. Gypsum bond plaster shall consist of not less 
than 93 per cent, of calcined gypsum and not less than 2, or more than 5 per cent., of 
hydrated lime. It shall not set in less than two hours or more than ten hours. The 
calcined gypsum plaster used in this specification shall have a purity of not less than 
66 per cent, by weight of CaS04 . |H 2 0. Gypsum ready-mixed plaster shall contain 
not more than 3 cu. ft. of mineral aggregate per 100 lb. of calcined gypsum plaster, 
to which may be added fibre and material to control working quality and setting 
time. However, when prepared for application to porous masonry bases it may contain 
not more than 4 cu. ft. of mineral aggregate per 1001b. of calcined gypsum plaster. Its 
setting time shall be not less than 1£ hours or more than eight hours. Gypsum neat 
plaster, which is mixed at the mill with other ingredients to control working quality 
and setting time, may be fibred or unfibred, the necessary aggregate being added 
at the job. Gypsum neat plaster when mixed with three parts by weight of standard 
sand shall set in not less than two or more than thirty-two hours, and when tested 
with two parts of standard sand shall have a compressive strength of not less that 
750 p.s.i. Gypsum wood-fibre plaster shall contain not less than 66 per cent, by 
weight of CaS04 . JH 2 and not less than -75 per cent, by weight of wood-fibre made 
from non-staining wood. It shall have a setting time of not less than 1 \ hours or more 
than sixteen hours and a compressive strength of not less than 1,200 p.s.i. Gypsum 
gauging plaster for finish coat is prepared by mixing with lime putty. The plaster 
shall contain not less than 660 per cent. CaS04.iH 2 by weight and shall have a 
setting time when not retarded of not less than twenty or more than forty minutes, 
and when retarded shall set in not less than forty minutes. As regards fineness the 



plaster shall all pass a No. 14 (1,410 micron) sieve and not less than 60 per cent, 
shall pass a No. 100 (149 micron) sieve. It shall have a compressive strength of not 
less than 1,200 p.s.i. 

Lime is frequently added to gypsum building plasters, but magnesian lime, if 
used, should be run to putty and left for three months to age before use. Eminently 
hydraulic limes are unsuitable for use in gypsum building plaster. The advisability of 
adding lime has, however, been questioned, particularly if the plaster coat is to be 
subsequently painted. 

Moulding Plasters. For use in the pottery industry it is essential that the plaster 
shall require as small a percentage of water for gauging as possible, so as to 
reduce the percentage of voids in the set plaster. This is sometimes attained by 
allowing the calcined gypsum to " age " for several months, whereby the amount of 
water required is reduced. A Canadian company, however, attains this end without 
ageing, by a process termed " aridizing " and consisting of spraying the gypsum, 
during calcination, with a small amount of a deliquescent salt. By this means 
gypsum plaster, which would require 80-90 per cent, of water when freshly calcined, 
only needs 60-70 per cent. 

Another form, known as " alpha-gypsum " also used for pottery moulds, is 
prepared by heating the gypsum, under pressure and without agitation, at 250° F., so 
as to produce dense, stubby-shaped crystals. This material, owing to the smaller 
surface area of its particles, only requires about two-thirds of the water needed for 
ordinary plaster to give a comparative consistency. 

A specification for gypsum potting plaster requires that it shall contain the 
equivalent of not less than 90 per cent, of calcined gypsum (CaS0 4 .4H 2 0) and 
have a setting time of not less than twenty or more than forty minutes. The ground 
product must all pass a 30-mesh (590 micron) sieve, and not less than 94 per cent, 
must pass a 100-mesh (149 micron) sieve. The gauged plaster must have a tensile 
strength of not less than 250 p.s.i. 

The A.S.T.M. Specification C 59-50 for gypsum moulding plaster requires a 
minimum content of 80 per cent, of calcined gypsum, all the material to pass a 30- 
mesh sieve and 90 per cent, to pass a 100-mesh sieve. Its setting time must be not less 
than twenty minutes or more than forty minutes, and its compressive strength not 
less than 1,800 p.s.i. 

Plaster for dental purposes should, as a rule, carry not less than 93 per cent, of 
calcined gypsum and it should all pass a 30-mesh sieve and 95 per cent, pass 100- 

Specification T 5-1951 of the Australian Standards Association for dental 
laboratory plasters requires the material to be of such fineness that all will pass a 
25-mesh sieve and not more than 5 per cent, be retained on a 100-mesh sieve. 
Setting time must be not less than five minutes or more than twenty minutes. The 
linear expansion of the gauged plaster must not be less than 05 per cent, and not 
over 0-2 per cent, at two hours after the plaster has developed its initial set. Tests 
are also specified for compressive strength of the gauged plaster and for strength 
during vulcanization. 

A modified form of calcium sulphate hemi-hydrate is prepared by heating 


Gypsum and anhydrite 

gypsum under pressure in the presence of water. The product differs somewhat from 
the usual hemi-hydrate and yields set products of higher strength. 

Acoustic plasters based on the hemi-hydrate usually contain an aggregate having 
sound absorbing characteristics, or are mixed with a foaming agent to give a porous 
mass on setting. 

Keene's cement, a plaster which sets slowly and has a hard and durable sur- 
face, may be prepared by treating plaster of Paris with a solution of alum or 
aluminium sulphate, drying and recalcining at a fairly high temperature. " Parian 
cement " is a product having similar properties but is made by using a solution of 
borax instead of alum. It can also be produced by calcining a mixture of raw gyp- 
sum and dry borax and grinding the calcined product. Other products of the Keene's 
cement type can be made by calcining gypsum at about 600° C. for several days, 
the mineral having been previously treated with a solution of some accelerator, such 
as potassium sulphate. 

Keene's or Parian cement is considered in B.S.I. Specification B.S. 1191 : 1955 
which deals with three grades intended for use as either (a) undercoat, (b) finishing 
or (c) dual purpose plasters. (See p. 241.) 

A.S.T.M. Specification C 61-50 for Keene's cement requires the product to 
consist of anhydrous calcined gypsum, the set of which has been accelerated by the 
addition of other materials. It should have a setting time of not less than twenty 
minutes or more than six hours. Its compressive strength should be not less than 
250 p.s.i., its fineness should be such that all will pass a No. 14 (1410 micron) sieve, 
98 per cent, a No. 40 (420 micron) sieve and 80 per cent, a No. 100 (149 micron) 
sieve. Combined water must not exceed 2 per cent. 

Anhydrite Plasters. The essential constituent of these hard finish plasters may be 
either natural anhydrite or a product obtained by the calcination of gypsum. When 
gypsum is calcined at temperatures above that required to produce the hemi-hydrate 
nearly all water is expelled and two general types of material may be produced, 
according to the temperature and time of calcination. At between 200 and 400° C. a 
so-called soluble anhydrite or anhydrous gypsum is obtained, which sets slowly when 
gauged with water, but calcination at temperatures between about 450 and 750° C. 
gives a product, sometimes termed artificial anhydrite, which has no setting 
properties when gauged alone with water. 

B.S.I. Specification B.S. 1191 : 1955 for anhydrous gypsum and anhydrite 
plasters recognizes two general types; (A) anhydrous gypsum plaster, and (B) anhy- 
drite plaster. Anhydrous gypsum plasters are subdivided into three groups according 
to their use; (a) undercoat plaster, (b) finishing plaster, and (c) dual-purpose plaster 
for undercoating and finishing. For either of the three types the specification requires 
a minimum content of 40 per cent SO3, with CaO not less than two-thirds of the 
percentage of SO3. The quantity of water-soluble sodium and magnesium salts, 
expressed as Na20 and MgO, must not exceed 01 per cent., and loss on ignition is 
limited to 3 per cent, of the weight of the plaster. Coarse particles retained on a No. 
14 B.S.I, sieve must not exceed 1 per cent. All three types have to comply with a test 
for soundness. Undercoat and dual-purpose plasters also have to satisfy a transverse 
strength test. 



Anhydrite plasters of the dual-purpose type, produced by grinding the natural 
mineral and adding a suitable material to accelerate the set, have to comply with the 
same requirements as anhydrous gypsum plaster in regard to chemical composition 
and coarse particles, except that the minimum for SO3 is 47 per cent, on the material 
as received. Anhydrite supplied for undercoat purposes also has to satisfy a trans- 
verse strength test. Plaster for finishing purposes has also to comply with the require- 
ments of a mechanical resistance test on the set neat plaster. 

Fireproofing. Gypsum plaster, on account of its combined water content (20 per 
cent.), is useful as a fire preventative. It is widely used as an insulating material for 
protecting columns or beams of metal or wood from high temperatures developed 
during a fire. A useful feature of gypsum blocks for this purpose is their freedom 
from expansion or contraction during large changes of temperature. Much useful 
information on the use of gypsum products in buildings has been published by F. C. 
Lea in his monograph on that subject. 

Paint Manufacture. As finely ground gypsum has a refractive index nearly the 
same as that of linseed oil, it is almost transparent in that medium, and hence is not 
generally suitable for use as a pigment in oil paints. The best-quality, finely-ground 
white gypsum is, however, much used as a base in cold water paints and distempers, 
and in the manufacture of certain of the cheaper grades of lake pigments. It is also 
sometimes used for diluting (reducing) highly coloured pigments such as chrome 
yellow, ultramarine and some iron oxides. Plaster of Paris is a basic ingredient of 
many plastic paints, a hardening agent being added to make the material more 

Chemically precipitated by-product calcium sulphate is a base upon which 
titanium dioxide is precipitated to produce titanium white pigment. It is also used 
with lead chromes, in place of calcium carbonate, to reduce the tendency to reddening 
in chrome yellow pigments. On account of its bulking properties and transparency 
in oils it is often employed in undercoat paints for use on porous surfaces. 

Artificial anhydrite made in the United Kingdom by calcining gypsum finds use 
as an extender in certain paints, notably those employed for making white traffic 
lines on roads. Several grades are produced, varying in colour from a good white to 
pink or even darker. One important user specifies a product not darker than a light 
brown in colour, in fine powder free from visible impurities, and having a loss on 
ignition not exceeding 1 per cent. 

The oil absorption of finely ground gypsum is about 21 as compared with about 
25 for anhydrite, and about 50 for chemically precipitated calcium sulphate. 

Portland Cement. Large quantities of gypsum are used for retarding the setting 
time of Portland cement, the amount used in Great Britain being about 2 per cent, of 
the cement produced. 

Providing that the gypsum carries a fairly high percentage of CaS04, the nature 
of the impurities present is of little importance. 

A common requirement in the United States is that the mineral shall contain 
about 42 per cent. SO3. A mixture of 75 per cent, gypsum and 25 per cent, anhydrite 
is sometimes used as a retarder in ordinary Portland cement. 

Ammonium Sulphate. The plants in operation at Billingham, England, for 



converting synthetic ammonia to sulphate of ammonia use anhydrite as the source 
of the sulphate radical, the process involving the interaction of ammonium carbon- 
ate and calcium sulphate. At the present time a large proportion of Great Britain's 
production of sulphate of ammonia, synthetic and by-product, is made by using 
anhydrite instead of sulphuric acid. Gypsum is also being so used at a factory near 
Calcutta, India. 

Sulphuric Acid Manufacture. The use of anhydrite as a source of sulphur for 
sulphuric acid or ammonium sulphate has been developed in Great Britain by 
Imperial Chemical Industries at their Billmgham plant which commenced operation 
in 1930. Similar plants are in operation in France, India, Poland and Germany. 

The annual capacities in terms of 100 per cent, sulphuric acid of the plants in the 
United Kingdom which utilize anhydrite are as follows: Imperial Chemical 
Industries Ltd., at Billingham, about 175,000 long tons; the United Sulphuric 
Acid Corporation Ltd. (an associate of I.C.I.) about 150,000 long tons; and Solway 
Chemicals Ltd., of Whitehaven, about 100,000 long tons. 

The anhydrite used by Imperial Chemical Industries Ltd. is obtained from a 
deposit 600-700 ft. from the surface within the factory area. This output covers the 
requirements of both the sulphuric acid and ammonium sulphate plants. The 
average composition of the run-of-mine product is 90-5 per cent, calcium sulphate, 
21 per cent, silica and 0006 per cent. salt. Mineralogical analyses show an average 
of 94-4 per cent, anhydrite plus water-soluble minerals, the remainder being musco- 
vite mica, 3-26 per cent.; biotite mica, 1 63 per cent.; paragonite, 0-35 per cent.; 
quartz, 017 per cent.; hornblende, 0-10 per cent., and fluorite 005 per cent. 

The process for making sulphuric acid consists essentially of heating together a 
mixture of anhydrite, sand, coke and aluminous ashes in such proportions as will 
yield a slag of Portland cement clinker with the evolution of all the sulphur as sul- 
phur dioxide. The operation is conducted in rotary kilns which attain a temperature 
of about 1,400° C. 

The kiln gases which contain about 9 per cent, of sulphur dioxide are then freed 
from dust by successive treatments in a cyclone, a water wash and an electrostatic 
precipitating unit. After being completely dried, the sulphur dioxide is converted to 
sulphur trioxide by means of vanadium or platinum catalysts: about 1 -64 tons of 
anhydrite are used for each ton of sulphuric acid produced, with a coal consumption 
of about 0-266 ton. The production of 1 ton of sulphuric acid also involves an out- 
put of 1 ton of cement clinker. It is generally considered that the smallest practicable 
plant would be one for about 50,000 tons of sulphuric acid per annum, but larger 
plants are to be preferred. A full account of the process has been given by W. L. 
Bedwell in a lecture to the Royal Institute of Chemistry. 

Brewing. Gypsum is sometimes added to the water used for brewing, for which 
purpose it should be of high grade and free from marl. Chemical analysis of one 
suitable product showed the following percentages: gypsum, 98; Si0 2 , 0-34- 
Al 2 03 + Fe 2 03, 0-34; MgO, 008; alkalis, 014; moisture and organic matter' 

Textiles. In the finishing of cotton and cloth, ground gypsum is often used to 
give weight to a product when a lustrous or glossy surface is required, It has but little 



covering power and is commonly used in conjunction with clay or talc to modify the 
effect produced by either. 

The gypsum should not contain more than 4 per cent, of calcium carbonate and 
for some purposes the limit may be 1 per cent. The amount of iron present should be 
low. A sample of gypsum suitable for use in cloth finishing was stated to have the 
following percentage chemical composition, CaS04, 77-42; CaCOs, 1 -45; Fe203, + 
AI2O3, 012; Si0 2 , 0-34; MgO, trace; NaCl, 0-26; and combined water, 20-46. It is 
stated that anhydrite is not suitable for use in cloth finishing owing to its hardness 
and darker colour. 

Paper Making. Both ground gypsum, known in the trade as " terra alba," and the 
calcined product, termed " pearl filler," are used to a small extent as fillers in the 
manufacture of certain writing papers, boards and specialities. 

Agricultural Uses. Fairly considerable quantities of crude low-grade gypsum and 
anhydrite are used for application to soils in many parts of the world. It is stated 
that their utility is principally to render certain black alkali soils suitable for arable 
use, particularly for the peanut crop in the South Atlantic States. The average 
amount applied for this crop is about 240 lb. per acre. The annual consumption in 
the United States exceeds 150,000 tons. In Great Britain smaller amounts are used 
under the name of " land plaster." 

Common grades of gypsum are largely used in the manufacture of artificial 
fertilizers, both as a carrier of the more concentrated chemical manures and as a 
drier for those containing liquid constituents, such as blood or animal offals. 

Insecticides. Ground gypsum, which has a bulking value of about 20 lb. to the 
gallon, is commonly used as a filler or distributor in many insecticides, white grades 
being most favoured. As the mineral is rather dense, for this purpose it is rarely used 
alone, but blended with a proportion of china clay. Both ground gypsum and 
anhydrite are, however, sometimes used as the sole distributing agent in certain 
agricultural preparations in order to minimize their dispersion by high winds. 
Finely ground anhydrite has been used for the control of weevil in grain. 

Other Uses. A specification for anhydrite to be used in the manufacture of 
leatherboard requires a product ground so that the residue on a 120-mesh sieve shall 
not exceed 3 per cent., with 10 per cent, residue on a 240-mesh sieve. The loss at 
105° C. must not exceed 3 per cent., and the limit for loss on ignition is 5 per cent. 

Calcium sulphate has been proposed as a substitute for elemental sulphur in the 
manufacture of certain explosives; the object being to eliminate, or reduce greatly, 
the formation of poisonous oxides of nitrogen and so permit mine-workers to 
return to a working place fifteen or twenty minutes after blasting. This use is covered 
by United States Patent No. 2,711,366, granted to S. A. Davidson and G. P. 
Sillitto and assigned to Imperial Chemical Industries Ltd. in 1955. 

Desiccants based on anhydrous calcium sulphate have been marketed in the 
United States for many years, but their successful preparation depended upon the 
selection of suitable raw material not generally available. Recently, however, a 
process has been developed by Hi-Drite Ltd. for treating raw material available in 
the United Kingdom to yield a " soluble anhydrite " suitable for use as a desiccant. 
The compound, which has the formula CaS04. JH2O, is claimed to have a drying 



efficiency intermediate between those of phosphorus pentoxide and concentrated 
sulphuric acid. Its chief characteristic is its capacity for drying under very dry 

Ground gypsum has been employed for some years for dusting in coal mines and 
it is used in the manufacture of blackboard chalks ; it is also a constituent of match 
heads, and has numerous other minor uses. 


" Gypsum: Its Uses and Preparation " By R. M. Santmyers. U.S. Bur. Mines, Inform. Circ. 

No. 6163, 1929, 28 pp. 
" Production of Sulphuric Acid from Anhydrite." By P. Parrish. Industr. Chem., 1929, 5, 491-3. 
" The Gypsum Industry of Canada." By L. H. Cole. Canad. Dept. of Mines, Mon. No. 714, 1930, 

164 pp. 
" Plaster-board." Science Library Bibliogr. Ser. No. 209, 1935. (54 references.) 
" Gypsum Plaster." Science Library Bibliogr. Ser. No. 208, 1935. (43 references.) 
" Relative Value of Gypsum and Anhydrite as Additions to Portland Cement." By P. S. Roller 

and M. Halwer. U.S. Bur. Mines, Tech. Paper No. 578, 1937, 15 pp. 
" Gypsum and Anhydrite." By F. T. Moyer. U.S. Bur. Mines, Inform. Circ. No. 7049, 1939, 45 pp., 

(including bibliography). 
" Expanding Markets for Agricultural Gypsum." By F. T. Moyer. Amer. Fert., 1942, 97, 6 and 18. 
" Plasters and Gypsum Cements for the Ceramic Industry." By J. S. Offut and C. M. Lambe. 

Amer. Ceram. Soc, Bull., 1947, 26 (No. 2), 29-38 
" Pottery Plaster and Its Applications." By T. P. Buckley. /. Canad. Ceram. Soc, 1948, 17, 

" Gypsum and Anhydrite Plasters." By H. Andrews. D.S.I.R. Nat. Building Studies, Bull. No. 6, 

1948, 16 pp. 
" Sulphuric Acid from Anhydrite." Anon. Industr. Chem., 1950, 26, 390-4. 
" The Sindri Fertilizer Factory." Anon. Industr. Chem., 1952, 28, 161-9. (Ammonium sulphate 

from gypsum ; flowsheets and diagrams.) 
" The Production of Sulphuric Acid from Calcium Sulphate." By W. L. Bedwell. Royal Inst. 

Chem., Mon. No. 3, 1952, 21 pp. 
" Modern Gypsum Processing Plant." By W. B. Lenhart. Rock Prod., 1949, 52, No. 7, 60-64. 
" Use of Gypsum Products in Building." By F. C. Lea. Building Res. Stat., note E. 162, 1950, 

19 pp. 
Gypsum and Anhydrite." By A. W. Groves. Overseas Geological Surveys, Lond., 1958, 108 pp. 

(including 16 pp. bibliography.) 
" Gypsum." By J. F. Havard. " Industrial Minerals and Rocks." Amer. Inst. Min. Met. Petrol. 

Engnrs., 1960, pp. 471-486. 
" Gypsum." U.S. Bur. Mines, Minerals Yearbook. (Annual) 

Standard Specifications 

American Society for Testing Materials 
A.S.T.M. Standards, 1958: 

Gypsum Moulding Plaster. C 59-50. 

Gypsum Plaster. C 28-58. 

Gypsum Concrete. C317-55. 

Keene's Cement. C 61-50. 
Australian Standards Association: 

Dental Laboratory Plaster. T 5-1951. 
British Standards Institution: 

Gypsum and Anhydrite Building Plasters. B.S. 1191 : 1955 



Hafnium has recently come into prominence on account of its constant association 
in nature with zirconium, and the difficulties encountered in preparing metallic 
zirconium fairly free from hafnium for use in atomic energy projects. All zirconium 
minerals contain hafnium. 

The mineral zircon may contain up to 7 per cent, of hafnium and in some 
secondary zirconium minerals such as alvite, malacon, cyrtolite, baddeleyite and 
zirkelite, the percentage may be as much as 35. 

Hafnium is a metal having a brilliant lustre and crystallizing in the tetragonal 
system. Some of the principal physical properties of hafnium are as follows : 

Atomic number 72 

Atomic weight . . . .178-54 

Crystal structure Close-packed hexagonal up to 1950 

± 10°C, above this temperature 
body-centred cubic. 

Melting point 2,130 ± 15°C. 

Boiling point 5400° C. 

Density (at 20° C.) .... 13-09 g./cm. 3 

0-473 lb./in. 3 

Thermal conductivity .... 0056 cal/sec./cm./°C. 

Thermal neutron cross-section absorption 

Microscopic 115 ± 15 barns*/atom 

Macroscopic ..... 4-71 cm. -1 

Specific heat (25-100° C.) . . 0-034 cal./g./°C. 

Coefficient of linear expansion (0-1 ,000° C.) 6-2 x 10- 6 per ° C. 

Electrical resistivity (at 0° C.) . . . 32 -4 microhm/cm. 

Young's modulus (at 23° C.) . . . 200 x 10 6 lb./in. 2 

Hardness (at 24° C.) .... 180 D.P.N. 

* 1 barn = 10" 24 cm. 2 

A useful summary of processes available for the separation of hafnium from 
zirconium has been given by D. R. Martin and P. J. Pizzolato in " Rare Metals 
Handbook," edited by C. A. Hampel. These processes include (1) the fractional 
crystallization of the hexafluorides, oxychlorides or oxalates; (2) fractional precipi- 
tation of phosphates or ethyl phosphates; (3) fractional decomposition of complex 
ions of zirconium and hafnium formed with various organic and inorganic acids; 
(4) fractional distillation of phosphorus oxychloride addition compounds of the 
metal tetrachlorides; (5) solvent extraction of complex compounds; (6) ion exchange 
methods; (7) adsorption methods; (8) selective reduction of ZrCl 4 to ZrCl 3 leaving 
volatile HfCl 4 . 

In a method patented by the U.S. Atomic Energy Commission (U.S. Pat. 
2,753,250) an aqueous solution containing the two metals as nitrates is extracted 
with an alkyl or aryl phosphate, preferably tributyl phosphate diluted with dibutyl 



ether, by which the zirconium is removed preferentially. A somewhat similar method 
has been described by some workers of the Commissariet a PEnergie Atomique 
under U.S. Pat. 2,757,081. A full account of three processes which have been 
operated on a large scale, with estimates of cost, have been given by J. B. Googin in 
" Progress of Nuclear Energy," Series III, Vol. 2. 


So far no important industrial applications have been found for metallic hafnium 
or its compounds, but the metal might possibly be used in the cathode of X-ray 
tubes, in electric resistance heating elements, in the form of a nickel-chromium 
alloy containing 0-5 per cent, hafnium, and in some special glasses. Research is in 
progress by the Metals Division of Imperial Chemical Industries to determine the 
best method for producing wrought forms of hafnium, with a view to their use as 
controlling agents in nuclear reactors. 

Considerable interest has been shown recently in the possible use of hafnium as 
a control material in nuclear reactors. The properties which make the metal of 
interest in this connection are its relatively high capture cross-section for thermal 
neutrons, its good resistance in water-cooled reactors and its high strength and 
resistance to irradiation and mechanical damage. 

Table 83A 

Composition of Hafnium Oxide and Metal, Wan Chang Corpn., U.S.A. 
Maximum metal impurities in p.p.m. 

Hafnium Oxide 



Grade I 

Grade II 

Sponge Metal 

Crystal Bar 

Aluminium, Al . 





Boron, B . 





Carbon, C 





Calcium, Ca 




Cadmium, Cd 





Chlorine, CI 




Cobalt, Co 





Chromium, Cr 





Copper, Cu 





Iron, Fe 





Lead, Pb 





Magnesium, Mg . 





Manganese, Mn 





Molybdenum, Mo 




Nickel, Ni 





Nitrogen, N 





Oxygen, O . 





Silicon, Si . 





Tin, Sn 





Titanium, Ti 





Tungsten, W 





Vanadium, V 





Zinc, Zn 





Zirconium, Zr 





Brinell hardness . 





The metal can be fabricated into flat shapes, cast tube or rod. It reacts readily 
with the halogens, oxygen, sulphur and nitrogen at elevated temperatures, but is 
unaffected at ordinary temperatures. 

Hafnium metal and oxide are produced by the Wah Chang Corporation of 
Albany, Oregon, U.S.A., to the extent of about 50,000 lb. per annum, mostly sold 
to the U.S. Atomic Energy Commission. Typical analyses of the metal and oxide, 
showing the maximum metal impurities, are shown in Table 83A. 

Hafnium oxide, specified to contain less than 2 per cent. ZrCh, is being produced 
in Great Britain by Magnesium Elektron Ltd. of Clifton Junction, Manchester. 

The research department of the Metals Division of Imperial Chemical Industries 
at Witton, Birmingham, are supplying hafnium strip metal for the pressurized 
water reactor core under construction by Rolls Royce Ltd. for a land-based proto- 
type in the British nuclear-powered submarine programme. 

Hafnium metal (powder), oxide, tetrachloride, sulphide, and nitrate have been 
offered for sale by the De Rewal International Rare Metals Co. in the United States. 


" On the Missing Element of Number 72." By D. Coster and G. von Hevesy. Nature, 1923, 111, 

" The Separation of Hafnium from Zirconium and the Production of Pure Zirconium Dioxide." 

By N. P. Sejin and E. A. Pepelyaeva. Proc. Int. Con/. Peaceful Uses of Atomic Energy, Geneva, 

1956, 8, 559. 
" Process for the Separation of Zirconium and Hafnium." By J. Hure and R. Saint- James, ibid., 

p. 551. 
" Zirconium Metal Production." By S. M. Shelton, E. D. Dilling and J. McClain, ibid., p. 505. 
" Hafnium." By D. R. Martin and P. J. Pizzolato in " Rare Metals Handbook," Ed. by C. A. 

Hampel. 1954, pp. 173-89. 
" Hafnium." By J. G. Goodwin and W. J. Harford. /. Metals. (N.Y.), 1955, 7, 952. 
" Preliminary Investigations on Hafnium Metal by the Kroll. Process." By H. L. Gilbert and 

M. M. Barr. /. Electrochem. Soc, 1955, 102, 243. 
" The Separation of Zirconium and Hafnium; Third Phase Formation in the Solvent Extraction 

from Aqueous Nitric Acid Solutions using Tributyl Phosphate in Various Dilutions." By 

J. Hudswell, J. C. H. Waldron and B. R. Harder. Atomic Energy Research Establishment, 

Harwell, 1957, 7 pp. 
" The Separation of Zirconium and Hafnium." By J. M. Googin. " Progress in Nuclear Energy," 

Series III, Vol. 2, 1958, pp. 194-209. 
" Hafnium Content and Hafnium-Zirconium Ratio in Minerals and Rocks." By M. Fleischer. 

U.S. Geol. Surv., Bull. 1021-A, 1955. 13 pp. 
"The Production of Hafnium." By H. P. Holmes, M. M. Barr and H. L. Gilbert. U.S. Bur. 

Mines Inf. Circ. 5769, 1955, 33 pp. 
" The Manufacture of Hafnium-free Zirconium." By F. Hudswell and J. M. Hutcheon. " Ex- 
traction and Refining of the Rarer Metals." Inst. Min. Met., 1957, pp. 402-419. 
" Hafnium." By C. T. Baroch in " Mineral Facts and Problems." U.S. Bur. Mines Bull., 585, 

1960, 6 pp. 
" Bimetallic Reduction of Hafnium Tetrachloride." U.S. Bur. Mines Rep. Invest. 5633, 1960. 
" Hafnium Bibliography." By S. Notestine. U.S. Bur. Mines. Inf. Circ. 7928, 1960. 


Although helium gas is found fairly widely distributed in nature, occurrences in 
percentages sufficiently large to be worth consideration from a commercial stand- 
point are very few. 



Helium was discovered by Sir William Ramsay and Lord Rayleigh in 1895 in the 
mineral cleveite and in 1905 it was first identified in a natural gas occurring at Dexter, 
Kansas, U.S.A. The gas is a constituent of the earth's atmosphere to the extent of 
about one part in 185,000. A comparison with the amounts (by volume in parts 
per million) of the other rare gases present in the earth's atmosphere, given by 
F. A. Paneth (1939), is as follows: Helium, 5 -24; Argon, 9-300; Krypton, 1 0; Neon, 
18; Xenon, 008. It is a minor constituent of many rocks and minerals and of some 
mineral springs and volcanoes, being usually associated with radioactivity. The 
helium contents of some typical radioactive minerals are as follows : 

cm? per gram 


. 10- 1-8 


. 0-8- 2-4 


. 3-5-10-5 

Cleveite . 

. 0-8- 8 

Helium has a lifting power 92 -6 per cent, of that of hydrogen, conducts electricity 
better than any gas except neon, has a low solubility in water and has the lowest 
liquifaction temperature of any known gas. 

The only natural sources of helium which have so far been exploited commer- 
cially are certain natural gases found in the United States, and as a rule the con- 
centration of helium is not over 1 per cent, by volume. In natural gas found in 
Europe the concentration is usually under 0-1 per cent. 

The helium-rich natural gases found in the United States occur principally in the 
following localities: 

Per cent, by volume. 
Los Animas, Colorado . . . .8-64 

Elk, Kansas 

McPherson, Kansas 

Isabella, Michigan 

Mussellshell, Montana 

Harley Dome Grand County, Utah 


It was stated recently that analyses of natural gas escaping from faults and 
fissures in underground gold-mine workings in the Witwatersrand, South Africa, 
had shown relatively high percentages of helium. 

The processes used for the separation of helium depend to some extent on the 
nature of the other components of the mixture. As an example, the mixture obtained 
from one well in Kansas contained the following percentages: helium, 1 -4; nitrogen, 
12-7; methane, 78-2; ethane, etc., 7-7. The gas issued from the borehole at a pressure 
of about 15 atmospheres. 

The process generally used to separate helium is to cool the mixture of gases 
below the liquifaction point of all the others, but above that of helium ( — 234-5° C). 
The helium so obtained, which has a purity usually between 98-2 and 99-5 per cent., 
is next passed through activated charcoal cooled in liquid nitrogen, by which its 
purity is raised to about 99-99 per cent. It is stored and shipped in high pressure 
welded cylinders, often at 2,000-2,400 p.s.i. pressure. 



A diffusion technique which may have important industrial applications for the 
separation of helium from natural gas mixtures, has been devised by K. B. McAfee 
and G. T. Kohman of the Bell Telephone Laboratories in New York. Briefly, the 
process consists in passing the helium-containing gas over the surface of a silica or 
pyrex glass which has a very high permeability for helium and very low for other 
gases, about 1,000 times greater than hydrogen at room temperatures. In order to 
obtain the requisite large surface area of glass a bundle of fine capillary tube is 
arranged so that the gas mixture flows around the outside of the tubing and the 
helium is recovered from inside the capillary, a high pressure differential being 
maintained between the two sides of the glass. If developed on a commercial scale 
the process should be capable of recovering large quantities of helium from natural 
gas which at the present time is being used only as fuel and not as a source of 

World Production 

Helium, from the time of its discovery in 1895 until the beginning of World War 
I, remained a scientific curiosity. It then began to receive attention as a non- 
inflammable light gas suitable for lifting airships, and its production from natural 
gas, sponsored by the U.S. Government, totalled about 200,000 cubic feet by the 
end of the war. The U.S. Bureau of Mines, in association with various commerical 
organizations, continued to investigate the economic production of helium from 
natural gas and took powers to control its sale and distribution. The U.S. production 
between 1921 and 1959 totalled over 3,000 million cubic feet, and in 1959 amounted 
to over 476 million cubic feet. 

In 1937 legislation authorized the U.S. Secretary of State for the Interior to sell 
helium for medical, scientific and commercial uses. The Helium Act, as amended, 
places the responsibility for conserving, producing and selling helium in the United 
States upon the Secretary of the Interior, acting through the Bureau of Mines. The 
Bureau operates four plants at Amarillo and Exell in Texas, Otis in Kansas and 
Navajo (Shiprock) in New Mexico. About 30 per cent, of the production goes to 
non-Federal uses, but directly or indirectly at least 90 per cent, of the production 
has benefited the Government. A new $12 million plant was commissioned in 
August 1959 for erection at Keyes, Oka. which will raise the total output capacity 
of the five plants to about 600 million cu. ft. per annum. 

The conservation of U.S. helium resources has received much attention and any 
production before 1953 in excess of current demand was conserved by injection into 
the government-owned Cliffside natural gas field near Amarillo. More recently 
large demands for supplies have necessitated withdrawals from the conservation. 

All the helium-bearing natural gases serving the Bureau's plants were located by 
drillings carried out by private companies in search of oil or fuel gas, but only a 
small proportion of the natural gas produced in the United States is used as a source 
of helium. At some plants helium is recovered from natural gas which would be 
unsuitable for use as a fuel owing to its high content of nitrogen. Hence, such 
plants only operate as the demand for helium requires. 

U.S. Government Regulations as revised in 1938 provided that helium disposed 



of for scientific use should be sold at a unit price per 1,000 cubic feet equal to 105 
per cent, of the actual cost to the Government, and that for commercial use the 
price should be 112 per cent. It was also provided that for medical use the price 
should be such as would in the judgment of the Secretary of the Interior, permit 
the general use of helium for such purposes. Only very small quantities of helium 
are exported and then only under special licence issued by the Secretary of the 

Great Britain's first liquid helium plant to be run by an industrial organization 
was started up, early in 1960, by the British Oxygen Research and Development 
Ltd., at Morden, Surrey. Formerly the National Physical Laboratory at Teddington 
had run a liquid helium plant, but it is understood that it is gradually discontinuing 
production and handing over its customers to B.O.R.A.D. The helium used will be 
imported from the United States. 


Helium is used by the United States Government in airships, meteorological 
balloons, atomic energy projects and guided missile operations. The chief non- 
government uses are for helium-shielded arc welding, leak detection, titanium 
metal production, and as an inert atmosphere in the production of germanium and 
silicon crystals for transistors. The use of helium as a shield permits arc welding 
of copper, aluminium, titanium, magnesium, stainless steel and other alloys to be 
done without the use of a flux or extensive pre-treatment. Helium is also used in 
de-gassing molten metals. 

The chief medical use for helium is as a diluent for oxygen to ease the breathing 
of asthma sufferers, a mixture of helium and oxygen being much lighter than air 
will flow more readily through restricted respiratory passages, thus permitting more 
oxygen to be breathed without increase in muscular effort. Helium-oxygen mixtures 
are similarly used by divers and caisson workers. Helium is finding an important 
use in the " Dido " research reactor at the U.K. Atomic Research Establishment at 
Harwell. Here part of the heavy water used as a moderator becomes split up by 
radiation into hydrogen and oxygen, which would form an explosive mixture if 
allowed to accumulate in the reactor. Helium is used as a carrier to remove these 
gases and after being so employed is purified for re-use by means of a drier and a 
carbon absorber, thus removing hydrogen, oxygen and nitrogen, but allowing helium 
to pass on. Helium is stated to be used as a coolant in the high temperature gas- 
cooled reactor system being investigated jointly by the twelve O.E.E.C. countries 
under the " Dragon " project. 

Helium under pressure is employed in the propellant-containing tanks of 
missiles using liquid fuel to replace the propellant and liquid oxygen as they are 
consumed and so maintain the rigidity of the entire missile. 


" Occurrence and Production of Helium in the U.S.A." By R. R. Bottoms, in " Science 

Petroleum," Oxford, 1938, Vol. 2, pp. 1517-1523. 
" The Upper Atmosphere." By F. A. Paneth. Quart. J. Roy. Meteorol. Soc, 1939, 65, 303. 
Helium. ' By W. H. Keesom, Amsterdam, 1942, 494 pp. 



' Helium." By R. D. Cattele and H. P. Wheeler, Jr., in " Encyclo. of Chem. Tech." by R. E. 

Kirk and D. F. Othmer. 1957, Vol. 7, 398-408. 
' Helium." By H. W. Lipper. U.S. Bur. Mines, Minerals Yearbook, 1958, 5 pp. 
' Helium-bearing Natural Gases of The United States, Analysis and Analytical Methods." By 

W. J. Boone, Jr. U.S. Bur. Mines Bull. 576, 1958, 117 pp. 
1 A Supplement to Helium." [By W. H. Keesom, 1942.] By E. M. Lifshits and E. L. Andro- 

nikashviti. (Translated from the Russian.) New York and London, 1959, 167 pp. 
' Helium and Other Inert Gases." By G. Pannetier in " Nouveau Traite de Chimie Minerale," 

Vol. 1, 1956, Ed. by P. Pascal, pp. 941-1072. 
' Helium." By H. W. Lipper and Q. L. Wilcox. " Mineral Facts and Problems." U.S. Bur. 

Mines Bull. 585, 1960, pp. 383-391. 
' Helium." By H. D. Keiser. " Industrial Minerals and Rocks." Amer. Inst. Min. Met. Petrol. 

Eng., 1960, 3rd Ed., pp. 617-8. 


The rare metal indium has received considerable attention during the past decade, 
particularly in the United States, on account of its low melting point and resistance 
to corrosion. 

Although a number of indium-bearing minerals have been described in the 
literature, none has been found in sufficient quantity to make extraction worth 
while on account of the metal alone. 

Indium occurs in many lead-zinc ores, particularly some found in the United 
States, Canada, Bohemia, Saxony and Sardinia, and in some tin, lead, tungsten, 
manganese and copper ores. Outstanding examples are the smithsonite ores of 
Virginia and Tennessee, U.S.A., which also contain the rare metals scandium, 
thallium and gallium. 

The amount of indium present in an ore may vary from a trace up to about 1 
per cent. Some ores, however, have been found to contain larger amounts, out- 
standing examples being the zinc ores worked in Mohave Co., Arizona, and the 
pegmatite minerals of Western Utah which contain up to 2-8 per cent, with 1 or 2 
per cent, of scandium. 

At the present time, the chief commercial sources from which indium is recovered 
are the flue dusts collected at some lead and zinc smelting works, and the cadmium- 
bearing residues obtained during the purification of zinc sulphate for use in litho- 
pone manufacture. Residues from the latter source may contain up to 2 oz. of 
indium per ton. 

World Production 

No reliable statistics of world production are available. Indium is produced in 
Canada by the Consolidated Mining and Smelting Co. of Canada at Trail, B.C. ; in 
the United States by the American Smelting and Refining Co., the Anaconda Copper 
Mining Co., the Cerro de Pasco Corporation at La Oroya, Peru. Production 
is also reported in Belgium, Germany, Japan and the U.S.S.R. The output from 
Canada in the years 1955, 1956, 1957 and 1958 was 104,774; 363,192; 384,360 and 



69,000 troy oz. respectively, 
about 35 tons. 

The potential annual production at Trial, B.C., is 

Extraction from Dusts, etc. 

Indium can be obtained from zinc-bearing flue dust by treating it with sufficient 
sulphuric acid to remove the zinc, leaving a residue containing indium, gallium and 
thallium, all of which can be recovered. This residue is dissolved in sulphuric or 
hydrochloric acid and the indium is precipitated as a crystalline basic sulphite, 
from which the commercial metal can be obtained by fusion with sodium and 
reduction in hydrogen, or by the electrolysis of solutions of its sulphate, fluoborate, 
chloride or sulphamate. 

The process evolved and used by the Cerro de Pasco Copper Corporation, Peru, 
for the extraction of indium from crude lead bullion is of interest. When the crude 
lead bullion is drossed to remove its content of 0-25 per cent, of tin, the indium is 
oxidized and concentrated in the dross. The dross is next totally reduced and the 
resultant metal is separated and then agitated, whilst molten, with small quantities of 
lead and zinc chlorides. This treatment converts the indium to the chloride, which 
passes to the slag, together with some lead, tin and zinc. The indium is removed by 
wet grinding the slag with a solution of hydrochloric and sulphuric acids. The 
filtrate from the pulp is purified from most metallic impurities by allowing it to 
stand in contact with metallic indium. The separated solution is next allowed to 
stand in contact with zinc rods, upon which the indium is deposited as a metallic 
sponge which can be removed, briquetted, melted under paraffin and cast into bars. 
The cast indium has a purity of 99-8 per cent, or over, the chief impurity being 
cadmium, with smaller amounts of lead, tin, thallium, copper and silver. In a useful 
publication, T. A. A. Quarm, of the Cerro de Pasco Copper Corporation, describes 
a method for obtaining high-purity indium from the commercial metal. The 
impurities present in the final product are lead, 0003 per cent. ; copper, 0002 per 
cent.; and silver, 00001 per cent., with an indium content (by difference) of 99-999 
per cent. 

Metallic indium is silver-white in colour, soft and ductile. It is unaffected by dry 
air at ordinary temperatures but rapidly oxidizes when heated above its melting 
point. It is not attacked by caustic alkali solutions, but is dissolved by strong 
mineral acids. Films of electrolytically deposited indium can take a high polish. 

Some of the physical properties of pure metallic indium are as follows : 

Atomic number 
Atomic weight 
Melting point. 
Boiling point . 
Density (at 20° C.) 

Thermal neutron cross-section absorption 
Crystal structure .... 
Naturally occurring isotopes (relative abundance) In-113, 4-23 per cent 

95 -7 per cent. 



156-4° C. 

2,000 ± 10° C. 

7-31 g/cc. 

190 barns 

Face-centred tetragonal 




Thermal conductivity 

Linear coefficient of expansion (at 20° C.) 

Modulus of elasticity 

Specific heat (at 20° C.) . 

Hardness (Brinell) .... 

0-057 cal./cm. 2 /cm./°C./sec. 

33 x 10- 6 /° C. 

1-57 x 10 6 p.s.i. 

0057 cal./g./° C. 


One of indium's most valuable characteristics is its property of diffusing into the 
surface of certain other metals at a relatively low temperature. 

The indium refinery operated by Mining and Chemical Products Ltd. at Alperton, 
Middlesex, England, has a capacity of over 50,000 troy ounces of refined metal per 
month. The raw materials used include residues from the refining of certain non- 
ferrous metals, e.g. zinc, and various crude indium bullions. Three grades of metal 
are produced containing respectively 99-95, 99-99 and 99-991 per cent, indium. 
Fabricated products made from the metal include tape, wire, discs, sheet, powder 
and shot. 

Refined metallic indium of 99-99 per cent, purity is also produced by Johnson, 
Matthey & Co. Ltd., of London, who also make a number of indium compounds, 
such as the oxide, hydroxide, trichloride, trifluoride, nitride, sulphate, sulphide and 
fluoborate. The same firm produces spectroscopically standardized indium oxide 
and chloride. 


Although a number of compounds of indium have been investigated, the com- 
mercial uses, at present, are all for the metal or its alloys. 

Semi-conductors. High purity indium is used in the manufacture of germanium 
transistors and rectifiers, and in the preparation of the semi-conducting compounds 
indium antimonide, indium arsenide and indium phosphide. Indium arsenide 
made for use as a semi-conductor by Metropolitan Vickers Electrical Co. of Trafford 
Park, Manchester, is claimed to have an exceptionally high mobility (30,000 cm. 2 / 
v./sec.) which is exceeded only by that of indium antimonide. It is claimed to be 
particularly suitable for devices based on the " Hall " magneto-resistance effect. 
An indium antimonide magnetometer is used to detect extremely small magnetic 

In the field of nuclear energy, since artificial radioactivity is easily induced in 
indium by neutrons of low energy, it can be used as an indicator in an atomic pile. 
Indium sulphate solution is potentially useful as a source of gamma rays in irradia- 
tion reactors for the preservation of food. 

Indium Plating. Indium can be electrodeposited upon many metals as a smooth 
matt surface which has good resistance to corrosion. As a general rule, only very 
thin deposits are required, often of the order of 00001 in. and it has been estimated 
that 1 sq. in. of metal can be so coated at a cost of less than Id. Deposits of indium 
on gold, silver, and copper can take a high mirror-like finish. 

Deposits upon lead, cadmium, zinc, tin, copper, silver and gold can be diffused 
into the metal by heating to about 180° C, with the production of a non-porous, 

M.C.A.I.— K 257 


corrosion-resistant, hard surface, a property which gives indium plating its chief 
commercial value. 

During World War II, extensive use was made of indium in the manufacture of 
bearings for internal combustion engines. A steel shell was given a lining of silver 
02-0 06 in. in thickness, and this was coated with lead which was plated with 
indium, the latter being later diffused into the lead by heat. It is stated that over 2J 
million bearings for aircraft engines were made by this process by one firm alone in 
the United States during World War II. It is suggested that similar bearings should 
be of value in automobile engines. The famous Vandervell bearing produced in the 
United Kingdom is an indium bearing. 

It is claimed that silver has the internal properties required to resist failure due 
to fatigue but it lacks the oiliness required in a good bearing surface. To overcome 
this a thin layer of lead is deposited over the silver surface. To protect this layer of 
lead from attack by organic compounds formed from lubricating oils and to pre- 
serve its surface wetability, a very thin coating of indium is electrodeposited and 
heat processed to diffuse the indium into the lead. 

Whilst the majority of aviation bearings are silver-lead-indium, other metals on 
to which indium can be plated and diffused, include copper, cadmium, zinc and tin. 

In addition to its use in bearings, indium can be deposited on a silver undercoat 
for decorative purposes, thus making the silver resistant to tarnish and increasing its 
hardness. The heat treated indium-silver surface can take a high polish and is resist- 
ant to wear. 

Indium has also been used for coating hollow steel propeller blades so as to 
give them a high degree of wetability. 

Indium Alloys. When indium or gallium is added to quaternary alloys of tin, 
bismuth, lead and cadmium, alloys of very low melting point are produced. Such 
alloys have been made by the Cerro de Pasco Copper Corporation. The composition 
and melting points of some of these alloys is shown in Table 84. 

Table 84 

Fusible Alloys Containing Indium 

Constituents (per 


Melting Point ° C. 















Cerroseal 35 . 





Cerrolow 147 . 








Cerrolow 136B 







Cerrolow 136 







Cerrolow 140 








Cerrolow 117 








Cerrolow 117B 








" Cerroseal 35 " is stated to be particularly useful for sealing glass to glass or 
glass to metal where high temperatures cannot be used. 



Indium, in amounts varying from 0-5 to 5 per cent., has been used in some dental 
alloys to give greater strength and resistance to corrosion. Its alloys are also employed 
in hinge pins for spectacle frames. Certain indium alloys have been used in special 
solders for brazing gold and silver plated articles. 


" Indium: Occurrence, Recovery and Uses." By R. E. Lawrence and L. R. Westbrook. Industr. 

Engng. Chem. {Industr. Ed.), 1938, 30, 611-4. 
" Electrodeposition of Indium from Sulphate Baths." By C. G. Fink and R. L. Lester. Trans. 

Electrochem. Soc, 1940, 78, 349-71. 
" Industrial Uses of Indium." By A. G. Arend. Chem. Age, 1945 (Oct. 6th), 313-5. 
" The Cerro de Pasco Enterprize, Metallurgical Research : Numerous Problems, including Indium 

Recovery." By T. R. Wright. Min. and Met., 1945, 26, 559-60. 
" The Rarer Metals." By J. de Ment, H. C. Dake, and E. R. Roberts, 1949, (Lond.), 345 pp. 

(Indium, pp. 22-33.) 
" Problems in the Production of Some of the Rarer Metals." By A. R. Powell. " The Refining of 

Non-ferrous Metals." Inst. Min. Met., (Lond.), 1950, p. 55. 
" A Bibliography of Indium, 1934-40." By M. T. Ludwick. Indium Corpn. of America, Utica, 

N.Y., 1940, 22pp. 
" Indium Plating." By H. B. Linford. Trans. Electrochem. Soc, 1941, 79, 443-52, including 

" The Extraction of Indium from Complex Lead-Tin Alloys." By J. Coyle. Trans. Electrochem. 

Soc, 1944, 85, 223-9. 
" Indium: An Unusual Metal doing an Amazing Job." Indium Corpn. of America, Utica, N.Y., 

1943, 7 pp. 
" Recovery of Indium." By C. C. Downie. Mining Mag. (Lond.), 1943, 69, 345-8. 
" Corrosion of Lead-Indium Diffusion Alloys." By J. M. Freund, H. B. Linford, and P. W. 

Schultz. Trans. Electrochem. Soc, 1943, 84, 65-70. 
" Indium." By W. S. Murray. Proc. 32nd Ann. Com. of Amer. Electroplaters Soc, June, 1944, 

11 pp. 
" A Method for the Preparation of High Purity Indium Metal." By T. A. A. Quarm. Inst. Min. 

Met. Bull. No. 529, 1950, pp. 77-80. 
" Indium from Rammelsberg Ores." By R. Kleinert. Mining Mag., 1950, 83, 146. 
" Indium." By A. A. Smith, Encyclo. of Chem. Tech. Ed. by R. E. Kirk and D. F. Othmer, 

1951, 7, 834. 
" Development of a Canadian Source of Indium Metal." By J. R. Mills, B. G. Hunt and G. H. 

Turner./. Electrochem. Soc, 1953, 100, 136-40. 
" Indium." By M. T. Ludwick, Indium Corp. of America, N.Y., 1959, 770 pp. 
" Semi-conductor Materials." By R. K. Willardson and T. S. Shilliday. Mater. Design Engng., 

1958, 47, No. 3, 114-8. „ ,„, 

" Indium." By D. E. Eilertsen, " Mineral Facts and Problems." U.S. Bur. Mines Bull. 585. 

1960, 4 pp. 
" Minor metals." U.S. Bur. Mines, Minerals Yearbook. (Annual) 
" Indium in Canada." Dept. of Mines and Tech. Surveys, Ottawa. (Annual) 


Iodine is found distributed very widely in nature, but usually in minute proportions 
only. It is a constituent of a dozen or so rare minerals which contain iodides of 
silver, mercury, lead, and copper, but none of these has been found in sufficient 
quantity to make it a commercial source of the element. 

The world's supply of iodine is obtained principally as a by-product from the 
refining of the caliche, or crude sodium nitrate, quarried in Chile. Smaller amounts 
have been obtained from certain deep oil-well borings and mineral springs in 
California, U.S.S.R., Indonesia, Japan and Italy. Although iodine occurs in sea- 

K 2 259 


water, the percentage present is so small as to make its recovery impossible as a 
commercial proposition, the average amount being about 25 mg. per ton of water. 

Extraction of Iodine 

Crude Chilean caliche, which is used principally as a source of sodium nitrate, 
also contains chlorides, sulphates, borates, perchlorates and iodates. The content of 
iodine, which varies with the deposit, ranges from 002 to 0-2 per cent., and averages 
about 015 per cent, in the material which is used for the extraction of iodine. The 
recovery starts with the mother liquors remaining after the crystallization of sodium 
nitrate in which iodine, in the form of iodate, occurs to the extent of about 6-12 gm. 
per litre. 

Two types of process are used in Chile for extracting the iodine. In the older and 
more generally used method, the iodine is precipitated by adding sodium bisulphite 
to the solution and the separated iodine is purified by resublimation. In the second 
process, gaseous sulphur dioxide is used as the precipitant. 

The waters from certain wells near Long Beach, California, contain iodate 
equivalent to 30-70 mg. per litre and are treated with sulphuric acid and sodium 
nitrate, liberating iodine which is absorbed by activated charcoal from which it is 
removed as sodium iodide. In the U.S.S.R. well waters from borings on the shores of 
the Caspian Sea are treated for their iodine content. 

Iodiferous waters used in Indonesia contain from 30 to 150 mg. of iodine per 
1,000 g. of water, the iodine being present as either sodium or magnesium iodide. 
In general the process used for extraction consists in pumping the waters to the top 
of gas-absorption towers: on their downward course they are met by an upward 
current of sulphur dioxide, which liberates iodine. The treated waters are run over 
bundles of copper wire and react to produce a precipitate of cuprous iodide, which 
is subsequently removed from the metallic copper by agitation in water. The 
cuprous iodide is separated, filter-pressed and after drying is ready for export. 
Potassium iodide is prepared from the material by fusing it with potassium car- 
bonate and lixiviating with water. 

In California iodine occurs in some oil well waters to the extent of 30 to 70 mg. 
per litre. Iodine has been recovered from these waters either by the activiated 
carbon or silver nitrate processes. In the carbon process the water is acidulated with 
sulphuric acid and iodine is liberated by the addition of sodium nitrite, and then 
caught by the activated carbon from which it is obtained by leaching with a solution 
of caustic soda. In the silver nitrate process the brine is treated with a weak solution 
of silver nitrate in calculated quantity necessary to precipitate all the iodine as 
silver iodide, ferric hydroxide being added to facilitate settling of the precipitate, 
which after being separated from the liquid is treated with concentrated hydro- 
chloric acid to dissolve the ferric hydroxide. The slurry of silver iodide is treated 
with steel scrap, resulting in the production of metallic silver and ferrous iodide 
from which iodine is extracted. 

In Italy, iodine is recovered from well-waters at Salsomaggiore near Parma, 
which contain about 50 mg. of iodine per litre in the form of magnesium iodide. 
The iodine, liberated by treating the water with sulphuric acid and sodium nitrite, 



is extracted by means of a petroleum solvent, from which it is subsequently liberated 
by treatment with sodium sulphite. 

World Production 

The world's production of iodine (excluding that from the U.S.S.R.) in 1957 
amounted to about 1 ,900 tons, of which about 1 ,200 tons was obtained from Chilean 
caliche, most of the remainder from iodiferous well-waters in California and Japan. 
Great Britain in 1958 imported 497 long tons of iodine. 

The quantity of iodine corresponding to the normal output of Chilean sodium 
nitrate would amount to about 12,000-15,000 long tons, but usually not more than 
10 per cent, is recovered. Hence, the Chilean iodine industry could readily expand to 
meet increased demands. 


The Corporacion de Ventas de Salitre y Yodo de Chile, which controls the 
marketing of Chilean iodine, specifies that all iodine marketed shall be of not less 
than 99 per cent, purity and have an acidity of not more than 0-1 per cent, calculated 
as H2SO4. As a matter of fact, however, the crude iodine now marketed by the 
Chilean producers has a purity of at least 99-5 per cent, and the resublimed product 
contains up to 99-75 per cent, iodine. The U.S. National Stockpile Specification 
P-24-R of May 23rd, 1956, requires that all iodine purchased shall contain 99 per 
cent, by weight of iodine and shall be heavy, greyish black plates or granules. 

The impurities found in commercial iodine may comprise chlorides, bromides and 
cyanides of iodine, and traces of various other inorganic compounds. 

Accurate statistics are not available, but it is estimated that about 66 per cent, of 
the world's production of iodine is used for medical purposes, either in the elemental 
form or as potassium iodide, 19 per cent, goes into technical industry, chemical 
teaching and research, and 15 per cent, is used in veterinary medicine and for addi- 
tion to animal feeding stuffs. 

Radioactive iodine-131 is widely used in biology, medicine and industry. A 
considerable amount of iodine is used in iodized salt for goitre prevention. Potas- 
sium iodide, sodium iodide and sodium iodate are used in special mixtures for the 
prevention of iodine deficiency diseases in cattle. A recent use for iodine is in the 
preparation of " iodophores," a variety of iodine-containing detergents. 

Industrial uses of iodine include the manufacture of some dyestuffs, certain 
electrical instruments (commutators and photoelectric cells), heat sensitive paints, 
light polarizing materials and special gas masks. Iodine and its compounds also find 
use in metallurgy, e.g. in the production of metallic titanium and zirconium; 
photography; in fire extinguishers; as improvers in bread making and in artificial 
rain-making (as silver iodide). At one time ethyl iodoacetate was used as a war gas 
under the designation K.S.K. 

The addition of iodine to salt intended for domestic consumption is dealt with 
under " Salt " (see p. 493). 

The consumption of iodine by industries in the United States is shown in 
Table 85. 



Table 85 

Consumption of Crude Iodine in the U.S.A.* 
Percentages of total 








Resublimed Iodine 







Potassium Iodide. 







Sodium Iodide . 







Other Inorganic Com- 

pounds . 







Organic Compounds 







Total (lb.) . 







* From " Minerals Yearbook," U.S. Bur. Mines. 

t Increased figures due partly to wider canvas of firms using iodine. 

A good account of the properties of a wide range of iodine compounds and their 
actual and potential industrial uses is given in " Iodine, Its Properties and Technical 
Applications," which was issued in 1951 by the Chilean Iodine Educational Bureau, 
New York. 


" The Production of Iodine in Chile." By J. B. Faust. Industr. Engng. Chem., 1 926, 18, 808-1 1 . 
" Bromine and Iodine." By P. M. Tyler and A. B. Clinton. U.S. Bur. Mines, Inform. Circ. No. 

6387, 1930, 26 pp., including bibliography. 
" Strategic Mineral Supplies." By G. A. Roush. (Lond.), 1939, 485 pp. (Iodine, pp. 377-95.) 
" Production [of Iodine] from Iodiferous Waters." Iodine Facts, No. 244, Iodine Information 

Bureau, London, 1946, 3 pp. 
" Iodine from Oil-well Brines." By F. G. Sawyer, N. F. Okman and F. E. Lush. Ind. Eng. Chem., 

1949, 41, 1547-1552. 
" Iodine, its Properties and Technical Applications." Chilean Iodine Educational Bureau, New 

York, 1951. 74 pp., including bibliography (330 items). 
" Iodophores, Properties and Applications." Iodine Information No. 50, Chilean Iodine Educa- 
tional Bureau, 1957, 18 pp. 
" Iodised Minerals." (For livestock.) Iodine Information No. 47, Chilean Iodine Educational 

Bureau, 1957, 24 pp. 
" Man-made Weather." (Silver iodide for rain-making.) " Iodine Facts," 465, Chilean Iodine 

Educational Bureau, 1951. 
" Iodine." By P. Pascal in " Nouveau Traite de Chimie Minerale," Paris, 1959, Vol. XVI, pp. 

" Iodine." U.S. Bur. Mines, Minerals Yearbook. (Annual) 
" Iodine Facts." Chilean Iodine Educational Bureau, London. (Numerous issues on the utilization 

of iodine.) 


U.S. National Stockpile Specification : 
Iodine P-24-R, May 23rd, 1956. 


Iron Ores 

Iron is the second most abundant metallic element in the earth's crust, in which it 
occurs to the extent of over 4-4 per cent. The most important naturally occurring 
ores of iron are the oxides; the carbonates and sulphides being of only relatively 
minor importance as ores of iron. Although a large number of minerals containing 
iron are known, only about half a dozen carry a sufficiently high percentage of iron 
and occur in masses of a size necessary for commercial exploitation. 

The most important iron ore minerals are the oxides, magnetite and hcematite, 
and the hydrated oxide, goethite (limonite). Of less importance are the carbonate, 
siderite or chalybite, and the sulphides, pyrite andpyrrhotite. In recent years ilmenite 
has been used in Canada as a source of both iron and titanium. 

The chief impurities in iron ores, as mined, are silica, alumina, titanium, sulphur 
and phosphorus. Silica may be present in the form of quartz, but often occurs as 
silicates, such as chamosite, a hydrated silicate of iron and aluminium. Titanium 
generally occurs in ilmenite or rutile; phosphorus principally in apatite, and sulphur 
in pyrite. Some iron ores also contain manganese, which may be useful in smelting. 
Chromium and nickel, which may occur in lateritic ores, may be objection- 

Iron ores occur in deposits of all geological ages, but most of the world's supply 
is obtained from Pre-Cambrian and Jurassic rocks. The principal types of deposit 
yielding iron ore are: (1) bedded ores, sometimes metamorphosed; (2) igneous 
segregations; (3) contact metamorphic deposits; (4) vein deposits; (5) super- 
ficial residues resulting from weathering; (6) bog and lake deposits of recent 
formation; (7) replacement deposits. The bedded ores are the most important and 
constitute a large proportion of the world's iron ore reserves — possibly over 60 
per cent. 

Magnetite, a black magnetic oxide of iron (Fe 3 C>4), contains when pure 72-4 per 
cent, of metallic iron. It has a specific gravity of about 5-4, a black streak, metallic 
lustre and hardness of 5J on Mohs's scale. It crystallizes in the cubic system, but 
most generally occurs in a massive, granular form. Magnetite is often found 
closely associated with varying amounts of aluminium, magnesium, titanium, 
sulphur, phosphorus, nickel, manganese, chromium and vanadium. Some mag- 
netite deposits carry the calcium phosphate mineral apatite, which can often be 
largely removed before smelting. Magnetite deposits usually contain some titanium, 
which may be so intimately associated with the iron ore that it cannot be separated 
by the usual ore dressing methods. 

Hcematite is a red sesquioxide of iron (Fej0 3 ) which, when pure, contains about 
70 per cent, of iron. It frequently occurs massive, but is occasionally found in very 
thin plates or scales and is then termed " micaceous " haematite. Haematite has a 
specific gravity of about 5 and a hardness of 5. It is usually black or reddish-black in 
the mass, has a reddish-brown streak and a high refractive index E = 2-94. 

Limonite is a general term applied to hydrated brown iron ore of variably 
specific gravity, usually about 3 -8. The mineral contains about 60 per cent, of iron 



free from impurities. It has a hardness of about 5£, a high refractive index, and 
becomes highly magnetic when heated in a reducing atmosphere. 

Goethite, a major constituent of many laterites is a hydrated ferric oxide, brown 
to red in colour, containing about 10 per cent, of water and 63 per cent, of iron. 
When pure its composition corresponds to the formula Fe 2 3 .H 2 0. Its specific 
gravity is usually about 4-2. 

Siderite, also known as chalybite or spathic iron ore, is a carbonate of iron which, 
when pure, corresponds in composition to the formula FeC0 3 , and contains 48-3 
per cent, of iron. The mineral commonly shows crystalline form, usually rhombo- 
hedral. It has a high refractive index, to = 1 87, a hardness of 4 and specific gravity 
of about 3-8. Owing to its isomorphism with the minerals calcite, magnesite and 
rhodochrosite it is often contaminated with calcium, magnesium and manganese. 
Deposits of siderite ore are usually of low grade and rarely contain more than 40 
per cent, of iron; they can, however, be considerably upgraded by calcining or 

Pyrite, a sulphide of iron with a formula FeS 2 , is of more importance as a source 
of sulphur (see p. 556) than iron, as it contains 46-5 per cent, sulphur. In recent 
years, however, the iron oxide sinter remaining after roasting off the sulphur (known 
as " burnt iron pyrites " or " pyrites cinder ") has received attention as a source of 
iron, and fair quantities are utilized in this way. The International Nickel Company 
has a large plant in Canada which is recovering magnetic iron oxide from pyrrhotite 
(Fe e S,) and sintering it to produce a high grade iron ore. 

Laterite. This name is applied to minerals consisting essentially of hydrated 
oxides of aluminium and iron: the latter, which usually predominates, may exceed 
50 per cent. Laterites have not so far been used to any considerable extent for the 
extraction of iron. One exception, however, is the laterite found at Nicaro, Cuba, 
which when dried contains about 50 per cent, iron and 1 -25 per cent, nickel. The 
ore, which has been worked extensively as a source of nickel, was the subject of 
large scale trials with a view to utilizing its iron content. Laterite from Conakry on 
the coast of Guinea, W. Africa, contains about 52 per cent, iron, is low in phos- 
phorus and other deletrious impurities, and is now being shipped to Europe and the 
United Kingdom. 

Titaniferous Iron Ores. As a general rule iron ore containing over 3 per cent, of 
titanium dioxide is not acceptable for smelting by ordinary blast furnace methods. 
By the use of a special process, however, very large tonnages of ore containing 
about 40 per cent, iron and 35 per cent, titanium dioxide are successfully treated for 
the production of pig iron, and of a slag from which titanium is recovered {see p. 
622). The ore consists of haematite so finely disseminated throughout ilmenite 
that the two minerals cannot be separated by any of the usual ore dressing 

A comprehensive account of iron-containing minerals is given in the monograph 
on "Iron Ore Minerals," published by the Ontario Research Foundation in 1958. 

Iron ores may be classified either according to their chemical composition or 
physical characteristics. On the basis of chemical composition, Bessemer grade ore 
should carry only 045 per cent, of phosphorus; over this amount the ore is often 



termed non-Bessemer grade. High phosphorus ores are those carrying over 018 
per cent, and siliceous ores normally contain over 8 per cent. SiO a . Ore classed as 
manganiferous usually contains over 2 per cent, of manganese, but some authorities 
take 5 per cent, as the upper limit for manganiferous iron ore. 

World Production 

The tonnage of iron ore marketed, including manganiferous iron ores, probably 
exceeds 450 million long tons per annum. Of this amount about 53 million long tons 
is produced in British Commonwealth countries. The largest quantities of iron ore 
marketed in recent years have been produced in the United States, the U.S.S.R., 
France, Canada, Sweden, Federal Germany, the United Kingdom, China and 
Venezuela (all over 15 million long tons per annum). The balance of location of 
supplies has changed considerably since 1939 and extensive new mines have been 
opened up, or are in course of development, in Venezuela, Peru, Chile, Labrador and 
French West Africa. Some ores, such as the taconites, which were previously 
considered uneconomic material for the blast furnace, have become important 
sources of supply. 

Iron ore mined in the United Kingdom is almost entirely Jurassic ironstone of 
low iron content, being in fact practically the lowest grade of iron ore smelted on a 
large scale. Hence, domestic production has to be augmented by imports from 
Sweden, North and West Africa, Sierra Leone, Newfoundland, Labrador, Brazil, 
Venezuela, Spain and France. Small quantities are also imported from a few other 

Countries importing the largest quantities of iron ore (in million tons) in 1957 
were the United States (33-6); Federal Germany (18-8); the United Kingdom 
(16 0); Belgium-Luxembourg (15-7) and Japan (9-3). 

The principal countries exporting iron ore, in order of importance, are Canada, 
Sweden, Venezuela, France, the U.S.S.R., the United States, Brazil, Chile, Peru, 
Spain, Algeria, Malaya, Liberia and India, all with over 2 million tons per annum. 
In addition a number of countries export burnt iron pyrites, the largest quantities 
coming from Italy, France, the Netherlands, Portugal, Sweden, Finland and Belgium- 
Luxembourg, all over 100,000 long tons per annum. 

The world's production of pig iron reached 217 million long tons in 1959, of 
which over 23 million long tons were made in British Commonwealth countries. 
The countries having the largest outputs are, in order of importance: the United 
States, the U.S.S.R., China, Federal Germany, the United Kingdom, France, 
Japan, Belgium, Czechoslovakia, Poland, Canada, Luxembourg and the Saar (all 
over 3 million long tons per annum). 

The world's output of crude steel in 1959 totalled nearly 300 million long tons, 
over 32 million long tons being produced in British Commonwealth countries. The 
United States and the U.S.S.R. together account for nearly 50 per cent, of the total, 
next come Federal Germany, the United Kingdom, France, Japan, Belgium, Italy, 
Czechoslovakia, Poland and China, all with productions over 5 million long tons 
per annum. 



Beneflciation and Processing of Iron Ores 

Only a moderate proportion of iron ore, as mined, is suitable for direct reduction 
in the blast furnace, owing usually to the presence of impurities which it would not 
be economic to feed into the furnace because of the large consumption of coke and 
flux required and the reduced output of pig iron, or to its physical condition. Up- 
grading of iron ores before smelting has been carried out for many centuries by 
processes varying from such simple methods as washing, jigging, drying and 
sintering to those involving fine grinding, and magnetic and heavy media separation. 
In the United States about 40 million short tons of beneficiated ore are shipped 
from the mines annually and account for over 40 per cent, of the total iron ore 
production of that country. 

Details of the many processes used to meet the requirements of different types 
of ore have been described in "Iron Ore Beneficiation" by L. A. Roe (1957). It will 
only be possible here to outline briefly a few typical examples. 

Probably the most important large scale beneficiation operations are those 
carried out on the taconites. A taconite may be defined as a ferruginous chert or 
shale in the form of a compact siliceous rock in which the iron oxide is so finely 
disseminated that practically all the iron-bearing particles are smaller than 200- 
mesh and it cannot be made saleable as an iron ore by any simple means of bene- 
ficiation, such as crushing, screening or jigging. Taconites may be roughly divided 
into two types (1) slaty, which requires grinding to micron size to liberate the iron 
minerals, a very costly procedure, and (2) cherty, of which two varieties occur, 
magnetic and non-magnetic, in which the iron mineral grains are coarser. The 
magnetic grade of the cherty variety is the one which has received most attention 

Enormous areas of taconites occur in Pre-Cambrian rocks in many parts of the 
world. Before the year 1940 such ores were considered to be normally unworkable 
for iron, although a beneficiation plant had previously been, and still is, operating 
at the Sydvaranger mine in Norway. Beneficiation processes have, however, been 
improved and developed and taconite ores are now worked on a large scale in the 
Lake Superior region of the United States and in Canada. Large deposits are also 
known to occur in Australia, Brazil, India, Norway, South Africa and Venezuela. 

Owing to its toughness, the rock is often difficult to mine and a special process of 
"jet piercing" has been evolved, involving the use of high-temperature jet flames in 
conjunction with a rotating drill. 

The ore as mined in the Mesabi range deposits of the Lake Superior region 
contain about 34 per cent, of iron and, by beneficiation, an ore is produced of the 
following average percentage grade: Fe, 61 -3; P, 009; SiO a , 9-8; Mn, 0-7; moisture, 

The process used to beneficiate taconites (largely magnetic taconites) consists 
briefly in crushing and grinding the ore, magnetic separation and final agglomeration 
of the separated ore. 

Calcination. Siderite ores are usually beneficiated by roasting before being 
shipped from the mine. When siderite is roasted it loses its carbon dioxide, and the 
ferrous oxide remaining is easily oxidized to magnetite or haematite. The two largest 



North American plants treating siderite are of the Algoma Ore Properties Ltd., in 
Ontario, Canada, and those of the Lone Star Steel Co. in N.E. Texas. The Canadian 
plant uses Dwight-Lloyd sinter machines to raise the iron content of the ore from 35 
to 51 per cent. The Texas plant uses a rotary kiln at 1,700-1,900° F. for the 
calcination of both siderite and goethite. In the case of the Algoma ore, calcination 
reduces the sulphur content from 2-42 in the ore before roasting down to about 05 
per cent. 

Calcination or drying at relatively low temperatures, are used to remove moisture 
and so reduce shipping weight of certain ores. Thus, Cuban laterites, as mined, 
contain 25 to 30 per cent, moisture and this can be reduced by means of a con- 
current rotary drier to under 3 per cent. The ore, as mined, contains about 50 per 
cent, of fines passing 325-mesh, and has to be dried before the lumps of ore can be 

Other Methods. Sink-float methods of beneficiation using magnetic media have 
found some favour in the United States, the preferred material being ferrosilicon 
containing about 85 per cent, of iron, but magnetite is sometimes used. 

From time to time chemical methods have been suggested for the beneficiation 
of low-grade iron ore. One example is the process tried out at the Appleby- 
Frodingham Works and described by L. Reeve (1955), in which the ore is treated 
with gaseous hydrochloric acid at 300-350° C, whereby all the iron is distilled 
off as ferric chloride, leaving the sulphur, phosphorus, calcium, magnesium, silica, 
etc., in the retort. The ferric chloride could then be hydrolysed by steam at 300°C. 
to give ferric oxychloride which at 550° C. gives ferric oxide, with the liberation 
of the HC1 gas which could be recycled. 

Agglomeration. One of the most important physical characteristics of an iron ore, 
from the smelting point of view, is the size distribution of the ore particles. If these 
are too coarse the reduction process is slow, and if too fine dust losses are high and 
furnace operations difficult. The success of most modern iron smelting processes 
depends largely upon the preparation of the ore before it is charged into the furnace, 
so as to secure uniformity of particle size of the burden. All fines below 10 mm. 
should be removed before smelting. 

For many years past the preparation of ore fines for use in the blast furnace has 
been accomplished by agglomerating processes. The four most common methods of 
agglomerating iron ore are: (1) sintering, (2) pelletizing, (3) nodulizing and (4) 
briquetting. All of these are expensive and fairly complex processes. 

(1) Sintering consists in the formation of a coherent cinderlike agglomerate by 
incipient fusion, usually carried out on continuous sintering machines. (2) In 
pelletizing, fine-grained ore minerals are rolled to form small spheres, which are 
next heat treated to bake them into hard pellets, f-lj- in. diameter. (3) Nodulizing, 
like sintering, uses partial fusion, but whereas sintering is a static process, nodulizing 
requires continuous relative movement between the charge and the processing 
equipment, usually a rotary kiln. (4) Briquetting of iron ore has never attained very 
large scale use and in recent years only one plant has operated in the United States. 

In 1958 iron ore agglomerates used in the United States totalled 35-9 million 
long tons, made up of sinter, 26-6; pellets, 8-5 million long tons, with much smaller 



amounts of briquettes and nodules. Most of the agglomerated ore was used in blast 

Smelting Iron Ore 

Metallic iron can be extracted from its ores by a variety of methods, but the one 
adopted almost universally is that of smelting in the blast furnace. Of much less 
importance are the so-called direct reduction processes. 

The blast furnace consists of a vertical shaft, 80 ft. or more in height, lined with 
firebricks and having a hearth diameter of up to 32 ft. Between 6 and 8 ft. from the 
base of the furnace are a number of openings through which are injected pre- 
heated blasts of air. The iron ore, mixed with carefully proportioned amounts of 
coke and limestone, is fed into the top of the furnace, where it meets hot reducing 
gases ascending from the lower part of the furnace. The proportions of material in 
the charge naturally vary with the composition of the ore to be smelted, but as a 
rough guide it may be stated that to produce one ton of pig iron from ore containing 
50 per cent, of iron it will be necessary to use 2 tons of ore, 5 cwt. limestone, } ton of 
coke and 3 tons of air. 

As soon as the charge starts to descend down the furnace, reduction begins. 
Reduction of the iron oxides is carried out by carbon monoxide in accordance with 
the reaction, Fe 2 3 + CO = 2FeO + C0 2 . At temperatures above about 950° C, 
the carbon dioxide formed is converted to carbon monoxide by carbon in the coke 
(C0 2 + C = 2CO). Thus more carbon monoxide is generated to complete the 
reduction in accordance with the reaction, FeO + CO-^Fe + C0 2 . The overall 
reaction at high temperature therefore becomes FeO + C = Fe + CO. Silica, 
alumina and other gangue materials react with limestone to form a slag. The molten 
iron and slag are tapped off separately at the base of the furnace, the iron being cast 
into pigs or more usually into ladles for subsequent steelmaking. 

The waste gases evolved from the top of the furnace have a CO/C0 2 ratio vary- 
ing from 2-5 to 1 -3 depending on the efficiency of the practice. The remainder of 
the gas contains a few per cent, of hydrogen and 55-60 per cent, of nitrogen. These 
gases, which have a calorific value of about 100 B.T.U. per cu. ft., are used in the 
works to pre-heat the blast and also for power purposes, although the calorific 
value is only about one-fifth that of coal gas. 

There is a demand in most countries for blast furnace slag, which usually varies 
between 7 and 25 cwts. for each ton of iron produced. Composition of blast 
furnace slag varies between the following percentage limits: SiO a 28-34, CaO 34-45, 
MgO 2-12, Al 2 O s 12-25, Fe 2 3 1-2, S 1-2-5. 

Sponge Iron. Much interest has been shown in recent years in processes for the 
direct reduction of iron ore to the metal without actually melting the metal. The 
product so obtained, which consists of a porous mass of reduced iron mixed with 
a certain amount of gangue, is termed sponge iron. It differs from wrought iron in 
that it is a mixture of iron and slag, whereas wrought iron contains a minimum 
amount of slag. Sponge iron can be used either as a raw material for treatment 
in the blast furnace or in steel making in electric or open hearth furnaces. 

Processes for making sponge iron which have been operated on a fairly large 



scale include the "Wiberg-Soderfors", the "Hogonas" and "HyL". In the Wiberg 
process high grade iron ore is reduced in a shaft furnace, a close control being kept 
on temperature and gas composition. 

The Hogonas process involves firing high grade magnetite surrounded by a 
mixture of limestone and coke breeze in ceramic saggers at a temperature of about 
1,200° C. for 8 days, and has been used in Sweden for many years to make about 
40,000 tons per annum of premium grade sponge iron for use in making special 
steels. A similar process has been developed in Canada by the Ontario Research 

In the HyL process, at present producing some 700 tons/day of sponge iron at 
Monterrey in Mexico, high grade iron ore is reduced with reformed natural gas in 
fixed beds at 850-1,000° C. The discharged sponge is then stored or charged direct 
to an electric melting furnace for conversion into steel. 

The Krupp-Renn process is intermediate between the blast furnace and sponge 
iron processes since incipient fusion occurs. It is mainly used for siliceous low grade 
iron ores which are charged with coke to a rotary kiln. Within the partially fused 
mass which occurs, the reduced iron agglomerates to form small nodules or 
" luppen ". After discharge, the iron/slag mixture is crushed and the iron is recovered 
by magnetic separation. 

Pig iron forms the primary material for the production of cast iron, wrought 
iron, malleable iron and the many varieties of ordinary and special steels. 

The classification of pig iron in the United States is largely based upon chemical 
composition. The American Society for Testing Materials recognizes 243 grades, 
which are divided into 8 classes. The American Iron and Steel Institute has a similar 
classification containing 236 grades in 10 classes. The classifications are based 
primarily upon content of phosphorus (which determines the class designation), 
and upon silicon content (which determines the grade within the classes). A summary 
of the A.S.T.M. classification is given in Table 85A. 

Table 85A 

Summary of A.S.T.M. Specifications for Foundry Pig Iron. A.S.T.M. A 43-557 





per cent. 









0035 max. 

0035 max. 

To 1-25 




Low-phosphorus . 



005 „ 

To 1-25 

1 00-3 -00 


Bessemer . 


0076-0- 100 

005 „ 

To 1-25 

1 00-3 00 





005 „ 






0-30 max. 

005 „ 





Low-phosphorus . 



005 „ 


To 3-50 


Foundry, Inter- 

mediate phosphorus 



005 „ 


To 3-50 


Foundry, High- 




005 „ 


To 3-50 



Cast Iron. This is pig iron which has been remelted and cast into moulds to give 
a wide variety of shapes for such articles as machinery parts, pump and valve 
bodies, chairs for rail tracks and many domestic articles, such as baths, grates, 
stoves, garden rollers, etc. In Great Britain the production of cast iron articles 
consumes about 1 5 per cent, of the total output of pig iron. 

The remelting of pig iron for making castings is usually carried out in a cupola 
furnace, using coke as fuel and adding a small quantity of limestone to flux the ash 
of the coke. 

The class of pig iron used varies according to the type of casting to be made. 
Thus, for castings which will cool rapidly in the moulds, a pig high in silicon (2-3 
per cent.) and high in phosphorus (1-1 -5 per cent.) may be selected. On the other 
hand, heavy thick castings do not require a high phosphorus pig, as the metal flows 
easily to all parts of the mould. The percentage of carbon also has an important 
bearing on the physical properties of the casting, but is rather difficult to control. 

In recent years a number of special cast irons have been made to meet certain 
requirements, such as increased tensile strength or corrosion resistance. Some of 
these involve the addition of silicon, either as ferrosilicon or calcium silicide, or the 
addition to the cupola charge of small amounts of alloys with other metals, such as 
nickel, chromium, copper, or molybdenum. Examples of nickel-containing cast 
irons are " Nicrosilal " and "Ni-resist ", the former containing 19 per cent, and the 
latter 12-15 per cent, of nickel. 

Attention has been given in recent years to the production of a variety of cast 
iron, which can be bent, and is known either as " nodular cast iron " or " ductile 
iron ". The material consists essentially of graphitic spherulites dispersed in a 
matrix of metallic iron. The two processes originally patented were (1) that 
developed by the British Cast Iron Research Association in 1946, which involved the 
addition of very small amounts of cerium, and (2) that described in 1947 by the 
Mond Nickel Co. Ltd., which depended upon the addition of magnesium to cast 
iron. Much work has been done in recent years on the production of ductile iron 
by the International Nickel Co. Inc. Full details of the properties of ductile iron will 
be found in the publications issued by the Gray Iron Founders Society of Cleveland, 
Ohio, U.S.A., in 1957. 

Specifications for ductile iron castings for various purposes have been formulated 
by the American Society for Testing Materials and published as A.S.T.M. A395- 
56T; by the American Standards Association and other bodies. 

Malleable Cast Iron. This material is produced by packing iron castings of selected 
composition into iron pots with red haematite iron ore and heating in a furnace for 
7 days or more at 950-1,000° C. This treatment causes the carbon in the cast iron 
to diffuse to the skin of the castings and then be removed by the oxidizing atmosphere 
induced by the iron ore. Other processes for making malleable cast iron are not 
designed to remove the carbon, but to precipitate it as nodules or specks throughout 
the metal. 

Wrought Iron. This was made by melting pig iron, with scrap, on the bed of a 
reverberatory or " puddling " furnace. It is essentially a fairly pure iron containing 
a number of parallel threads of slag, which give the material a fibrous appearance. 



Owing to its very low content of carbon it does not harden when quenched, but 
remains tough and malleable and can be rolled into plate or drawn into wire. 
Wrought iron has for many years been largely superseded by steel, but is occasionally 
used for special purposes when good welding and corrosion resistant properties are 

Ferro-alloys. A large number of alloys of iron with other metals finds use in 
industry, and are dealt with in this volume in chapters dealing with the non-ferrous 
constituents, e.g. boron, chromium, manganese, niobium, tantalum, phosphorus, 
silicon, vanadium and zirconium, etc. Mention must be made here, however, of 
"silvery iron", a high silicon pig iron containing from 9 to 20 per cent, of silicon. It 
can be produced in the blast furnace or in the electric furnace. In the United States 
silvery iron made in the blast furnace contains on the average 8 -7 per cent, of silicon, 
whilst the electric furnace product averages about 15-9 per cent. 

In 1958 the United States produced 246,948 short tons of silvery pig iron which 
was classified into two groups containing respectively 5 to 13 and 14 to 20 per cent, 
of silicon. The consumption of the first group totalled 1 10,392 short tons, about 85 
per cent, of which was used in iron foundries and the remainder in steel ingots or 
castings. Of the production of the second group, totalling 136,556 short tons, 
about 56 per cent, was used in steel ingots and about 40 per cent, in iron foundries. 

Increasing amounts of silicon have an important bearing on the properties of 
cast iron and a number of special acid-resisting alloys have been developed for 
chemical plant. Normal acid-resisting silicon iron should contain at least 14 per 
cent, silicon and British Standard Specification No. 1591 suggests between 14-25 
and 15-25 per cent. 

The composition of a number of silicon irons sold under trade names is shown 
in Table 85B. 

Table 85B 
Composition of High Silicon Irons* 

Composition (per cent, by weight) 








Tantiron E 
Le Creusot 
B.S. 1591 






















* From Chemical Engineering Materials, by F. Rumford, Lond., 1954, p. 219. 
t Also contains Mo 3-5-4 per cent. 

Rumford states that all the irons in Table 85b are casting alloys with a Brinell 
hardness of at least 450 and extremely brittle. Specifications for silicon iron are 
discussed by Rumford; in general the metal is used extensively in sulphuric acid 



concentration plants and where resistance to heat, as well as corrosion, is required. 

" Silals " are a group of heat-resisting cast irons patented by the British Cast 
Iron Research Association (B.P. 323,076). They contain 5 to 10 per cent, of silicon, 
very little combined carbon, and can be used up to about 850° C. without any serious 
attack by air. 

Blastfurnace slag is marketed in four general classes : ( 1) air-cooled and screened ; 
(2) air-cooled, unscreened; (3) granulated; and (4) expanded, the greatest proportion 
being in the first category. The air-cooled screened product is used principally in 
highway surfacing, manufacture of concrete blocks, Portland cement concrete 
construction work, and to a much smaller extent in mineral wool, roofing granules 
and in sewage filter beds. 

The granulated slag is mostly used in highway construction and in the manu- 
facture of hydraulic cement. Expanded slag is used as an aggregate in concrete block 
manufacture and in lightweight concrete. Specifications for Portland blast-furnace 
cement are considered in the chapter on Limestone. 

Mineral wool made from blast furnace slag finds use for heat insulating and as a 
packing material. 


A vast amount of literature is available regarding details of modern methods 
used on a large scale for the conversion of pig iron and scrap into steel. It will only 
be possible here to give a brief outline of even the more important processes. For 
greater detail the text book " The Manufacture of Iron and Steel ", vol. 2 Steel 
Production by G. R. Bashforth (1959) will serve as a useful introduction to this 
complex subject. 

The three principal types of processes used on a large scale are: (1) converter; 
(2) open-hearth; (3) electric furnace. All three methods can be carried out in either 
acid or basic lined furnaces, and are subject to variations. The old-fashioned 
cementation process is no longer used and the crucible method is only used to a 
relatively small extent to produce special quality steel. 

In the converter processes liquid pig iron is refined by blowing air or oxygen 
through or upon the metal. The classical Bessemer converter is bottom-blown with 
air and may have an acid (siliceous) or basic lining. The latter is more common 
since high phosphorus iron can be refined by the addition of lime to remove the 
phosphorus as a phosphate slag. 

The advent of cheap tonnage oxygen has led to a number of modifications of the 
converter process, including the oxygen/steam and oxygen/CO a bottom-blown 
process, the top-blown L-D and the Kaldo and Rotor processes. Rather more scrap 
can be tolerated in the newer processes than with the air-blown Bessemer converter 
and the quality of the steel is comparable with open hearth steel since there is an 
absence of nitrogen in the blast. 

In the open hearth process pig iron, together with scrap, or rich iron ore, is 
melted in gas or oil fired furnaces, the oxidation of the impurities being effected 
partly by the oxidizing flame and partly by the iron ore in the molten bath. Any 
proportion of scrap to pig iron can be used in this process. 



In electric furnace processes the necessary heat is supplied either through elec- 
trodes (arc furnaces) or by induction (high frequency furnaces). The iron is refined 
either by adding ore to the molten charge or by blowing oxygen through the mass. 

In addition to the output obtained by the above methods, smaller quantities of 
steel for special purposes are made by the crucible process, a method used extensively 
before the invention of the Bessemer process. In the crucible process for cast steel, 
bars of wrought iron are melted with a calculated amount of carbon in fireclay 
crucibles, whereby the iron is slowly converted to steel by absorbing carbon, the 
time required for the operation being about 4 hours. 

Adequate supplies of ferrous scrap are essential for modern steel making. The 
ratio of scrap to pig iron used varies with the type of process. The averages used in 
the United States in 1957 were as follows: 


Scrap iron 

Pig iron 






Bessemer* .... 

19 3 


Electricf .... 



Cupola .... 






* Includes oxygen-steel furnaces. 
t Includes crucible furnaces. 

In recent years an ever increasing use has been made of oxygen in iron and steel- 
making with a view to obtaining a higher output per furnace per day. Oxygen may 
be used for treating molten metal in converters, open hearth furnaces or electric 
furnaces. The practical aspects of the use of oxygen in iron and steel making have 
been very adequately dealt with by Charles, Chater and Harrison of the British 
Oxygen Co. Ltd. (1957). 

According to G. R. Bashforth (1959) the composition of pig iron suitable for 
making high quality steel by the commonly used processes should be within the 
limits shown in Table 85C. 

Table 85C 

Pig Iron for Steel Making 

Range in Composition — per cent. 







Acid Bessemer 
Basic Bessemer 
Acid Open Hearth . 
Basic Open Hearth . 

3 0-3-6 



1 -0 max. 

0040 max. 
0050 max. 

0040 max. 
0050 max. 
06 max. 

10 -2-5 
2-5 -30 
10 -3 

Methods for making steel direct from iron ore have been explored from time to 
time, but none has yet been successfully developed. 



Types of Steel 

In view of the great diversity in composition and physical properties of steels 
available to industry, it is only possible to mention here a few general types. 

Steels may be classified according to their chemical composition, mechanical 
properties, special physical properties, such as resistance to corrosion or heat, or 
by uses. 

As carbon is an element which largely affects the properties of steel, the per- 
centage of this substance present often serves to divide steels into grades according 
to their uses. 

Mild Steel, which possibly constitutes about 90 per cent, of Great Britain's 
production of plain carbon steel, contains 01-0-25 per cent, carbon and 0-5-0-7 per 
cent, manganese. 

High Tensile Steels. These may be roughly classified into: (1) silicon steels, 
which may contain up to 0-4 per cent, carbon; (2) manganese steels with up to 1 -25 
per cent, manganese; (3) steels of somewhat similar composition to those of 
group (2) with the addition of 0-25-0-5 per cent, copper, which have special resist- 
ance to corrosion; (4) steels alloyed with manganese, chromium and copper. In 
addition, there are a number containing niobium, nickel, molybdenum, titanium or 

Structural Steels. Steel framed buildings generally utilize one of the following 
types of steel: (1) mild steel conforming to British Standard Specification B.S. 15; 
(2) high tensile steel conforming to B.S. 548, or; (3) a special high tension fusion 
welding quality made to conform to B.S. 968. A number of alloy steels are also used 
for special purposes. 

Stainless Steel. Composition of this range of products may vary between the 
following percentage limits: Cr, 13-25; Ni, 2-20; C, 0-1-0-3; Mo, 0-3. 

A large variety of stainless steels has been developed for special purposes. 
These include: (1) Martensitic or hardenable steels containing about 18 per cent. 
Cr, and 2 per cent. Ni; (2) Ferritic stainless steels which contain from 14-22 per 
cent. Cr, but only about 0-07-0- 11 per cent. C, and; (3) Austenitic steels, which are 
ductile, non-magnetic and are softened by quenching; this group, which includes 
the well known 18/8 class (18 per cent. Cr/8 per cent. Ni), have better corrosion 
resistance than either the martensitic or ferritic class. 

Tool Steels. These may be divided into three groups, i.e. carbon, alloy and high- 
speed. In carbon tool steels, the oldest of this class, increasing carbon content 
increases the hardness but reduces the toughness. The carbon content varies con- 
siderably and ranges from about 0-5 up to about 1 -3 per cent. 

Alloy tool steels contain variable proportions of manganese, nickel, tungsten, 
chromium, molybdenum and vanadium, the elements being added to increase the 
natural hardness of the steel and to improve some physical properties, such as 
retention of hardness at high temperatures. 

In high-speed steels required for tools to be used at high cutting speeds without 
losing their cutting efficiency or wearing away too rapidly, the principal alloying 
element is tungsten, with variable amounts of chromium, vanadium, molybdenum 


raoN ORES 

and cobalt. In general, the percentage of tungsten plus twice the percentage of 
molybdenum is not less than 12. 

Magnet Steels can be roughly divided into two classes: (1) those for permanent 
magnets, which will retain their magnetism, and (2) those for magnets which can be 
readily magnetized and demagnetized. Permanent magnetic alloys may be marten- 
sitic steels including plain carbon steel, chromium steel (about 3-5 per cent. Cr), 
tungsten steel (6 per cent. W) or steels with 3-35 per cent, cobalt. The more 
modern permanent magnetic alloys contain Al, Ni, Co, Cu, Ti or other elements, 
in addition to iron, and are given their magnetic properties by precipitation harden- 
ing. Some of these alloys are marketed under trade names such as ALNIa, ALNICOa, 
Alcomax, Ticonal and Hycomax. 

Steels included in the second group have some properties rather the opposite of 
those of the permanent magnet type; they must be easily demagnetized and retain as 
little magnetism as possible, but they must be very permeable to magnetism and 
absorb a minimum of energy in an alternating magnetic field. These steels usually 
contain very little carbon or sulphur (usually about 0012 and 0006 per cent, 
respectively) but no alloying elements, except about 1-4-5 per cent, of silicon, 
which is essential for the development of their properties. 

Gas Turbine Steels. The widespread development of the gas turbine has resulted 
in a demand for steels which will retain their more important physical properties 
at relatively high temperatures. Such steels may be roughly divided into three 
classes: (1) ferritic, or pearlitic, non-austenitic steels suitable for use at temperatures 
not exceeding about 600° C. An example of this class is the alloy steel H40 which 
contains chromium, tungsten, molybdenum and vanadium, and has been used for 
high temperature resistance to hydrogen embrittlement — as in turbine discs. (2) 
This group includes ferritic and austenitic alloy steels ranging from 6 per cent, 
plain chromium steel (used as a valve steel for low pressure internal combustion 
engines) up to 65 per cent, nickel/18 per cent, chromium steel intended for use under 
particularly corrosive conditions. (3) This group includes austenitic alloys having 
high creep strength at temperatures above 600° C. This class includes the well known 
18/8 stainless steel and the later developed types, such as the "stellites" and "ni- 
monic" alloys. 


The types of iron utilized by the chemical engineer include grey cast iron, white 
iron, malleable iron, low-alloy grey iron, martensitic iron, high chromium iron, 
acicular iron and, corrosion resisting iron of the high silicon type. The general 
characteristics of these numerous grades and their suitability for specific purposes in 
chemical industry have been discussed by Riley, Park and Southwick (1950) who 
give much useful data concerning the resistance of these metals to heat, corrosion 
and attack by a number of chemical compounds. 

Mild steel is the metal used in greatest tonnage in chemical process vessels and 
structural plant. Low-alloy steels are used where a material of higher tensile strength 
than mild steel is required, or where the addition of the alloying elements gives extra 
resistance to a particular type of corrosion. High nickel austenitic cast irons are 



used extensively for chemical plant required to handle alkali and certain acids. 
High-alloy steels are used where resistance to corrosion is required and much use is 
made in chemical industry of chrome and chrome-nickel steels of the austenitic 
type with or without the addition of titanium. 

Non-Metallurgical Uses for Iron Ores and Metallic Iron 

Some iron-bearing materials find uses in industry for purposes other than 

The mineral haematite (Fe 2 3 ), in addition to being a valuable iron ore is also 
used in chemical industry. Certain massive types of the ore give a fine red ochre 
pigment when ground and these are discussed in the chapter on Ochres, Umbers 
and Other Mineral Pigments. A variety known as micaceous haematite, so named 
on account of its platy character, has special uses as a protective pigment (see p. 441) 
and as a coating for electric welding rods. For this latter purpose mineral which is 
too hard in texture to permit its use as a pigment is quite acceptable, providing that 
its content of phosphorus and sulphur are low. A fairly high content of silica is 
permissible. Suitable material may have the following approximate percentage 
composition: Fe 2 3 , 92; Si0 2 , 6; P, 0015, and S, 0015. 

Bog iron ore is often used to remove sulphur from coal gas. 

The desirable characteristics of bog ore for this purpose are that it should be 
friable and easily crumbled, not clay-like, fairly free from roots and have a very fine 
ultimate particle size. 

The most suitable ore is one having a high content of moisture without any 
tendency towards sogginess. The composition of a suitable bog ore is stated to be as 
follows: hydrated iron oxide, Fe 2 3 .HjsO, 60-65 per cent.; organic matter, 15-25 
per cent.; silica, 3-6 per cent.; alumina, 1 per cent. The above analysis is on a dry 
basis, the ore before drying containing from 50-60 per cent, water. During World 
War II, Burnt Island red was used as a substitute for imported material. This 
product contained about 56 per cent. Fe 2 3 ; 15 per cent. A1 2 3 ; 8-5 per cent. SiO, 
and 6-5 per cent. Na a O, all calculated on a dry basis. It was found to be relatively 
inactive owing to the presence of sodium aluminium silicate, but could be activated 
by treatment with acid. 

The magnetic tape recording industry uses fair quantities of gamma haematite, 
which may be produced by the controlled oxidation of magnetite or by chemical 
processes. A summary of some methods available has been given by M. Camras in 
U.S. Pat. 2,694,656 of Nov. 16th, 1954. 

One of the oldest processes for the production of hydrogen, which is still used 
commercially to a small extent, consists in reducing iron ore by means of producer 
gas or water gas, and treating the product with steam. 

A fairly recent use for either magnetite, cast iron or steel is in the production of 
high density concrete for shielding atomic energy plants. Comprehensive accounts 
of this use have been given by Davis, Brown and Witter (1956) and by Davis (1958). 

Iron is fairly widely used as an abrasive in some "sand blasting" processes for 
cleaning or preparing surfaces of iron and steel foundry castings, and a wide variety 



of mill products. It may be in the form of chilled or annealed iron shot or grit, steel 
shot, or in some other form such as cast-wire shot. 

Iron scale derived from rolling mills, has been used in the production of special 
catalysts for use in the Fischer-Tropsch synthesis of petrol. 

Compacted iron powder was formerly used in loading coils employed to correct 
frequency distortion and attenuation in underground telephone cables, but this 
material has been largely superseded by ternary alloys incorporating either molyb- 
denum or copper, or by oxide materials based on a spinel type of crystal structure 
termed "ferrites ". 


" Magnetic Separation of Ores." By R. S. Dean and C. W. Davis. U.S. Bur. Mines Bull. 425, 

1941, 47 pp. 
" Lean Ores; German Experience in their Preparation." By W. Lukyen. Iron and Steel (Lond.), 

1947, 471-5. 
" Review of Ferrous Metals used in the Chemical Industry." By N. P. Inglis in " Materials of 

Construction in the Chemical Industry." Society of Chemical Industry (Lond.), 1950, 

pp. 91-103. 
" Creep- and Heat-Resisting Steels for the Chemical Industry." By E. W. Colbeck and C. V. 

Mills. Ibid., 105-111. 
" Cast Iron and High Silicon Acid-Resisting Iron." By R. V. Riley, J. R. Park and K. Southwick. 

Ibid., 113-124. 
" The Selection of Ferrous Metals for the Oil Refining and Petro-Chemical Industry." By Ir. 

W. P. Kerkhof, N. G. Geerlings and Ir. H. van der Haas. Ibid., 125-138. 
" Stainless Iron and Steel." By J. H. G. Moneypenny. 3rd Ed. (Lond.), 1951, 352 pp. 
" Steel in Modern Industry." Ed. by W. E. Benbow (Lond.), 1951, 562 pp. 
" Steels for Chemical Industry." By N. P. Inglis. Ibid., 291-304. 

" Gas Turbine Steels and Alloys." By D. A. Oliver, G. T. Harris and W. H. Bailey. Ibid., 215-237. 
" Pressure Vessels." By H. N. Pemberton. Ibid., 279-299. 
" Resources for Freedom." Report of the President's Materials Policy Commission (Washington, 

D.C.), 1952. 
" Iron Making for High Sinter Burdens." By G. D. Eliott, J. A. Bond and T. E. Mitchell. /. Iron 

and Steel Inst., 1953, 175 (3), 241-247. 
" The Sintering of Iron Ores." By J. M. McLeod. /. Iron and Steel Inst., 1954, 103-109. 
" Sponge Iron and Direct Iron Processes." By E. P. Barrett. U.S. Bur. Mines Bull. 579, 1954, 

143 pp. 
" Magnetic Impulse Record Processes; Magnetic Material and Method of Making Magnetic 

Material." By M. Carreras. U.S. Pat. 2,694,656, Nov. 16th, 1954. 
*' Open Pit Taconite Mining at Mesabi, U.S.A." By J. Grindred. Min. Jour. (Lond.), 1955, 245, 

" Bibliography of the Iron Ore Resources of the World to January, 1955." By G. W. Luttrell. 

U.S. Bur. Mines Bull. 1019D, 1957, 183 pp. 
" Development of Chemical Treatment of Low Grade Iron Ores at Appleby-Frodingham." By 

L. Reeve. /. Iron and Steel Inst., 1955, 181 (Pt. 1), 26-40. 
" Survey of World Iron Ore Resources, Occurrence, Apprisal, and Uses; Report of a Committee 

of Experts appointed by the Secretary General." United Nations, Dept. of Economic and 

Social Affairs (New York), 1955, 345 pp. 
" Iron." By R. W. Holliday in " Mineral Facts and Problems ". U.S. Bur. Mines Bull. 556, 

1955, 28 pp. 
" The Ore Dressing Plants of Sydvaranger A.S., Norway; The Mining and Dressing of Low 

Grade Ores in Europe." By J. K. Johannesen. Report by O.E.E.C. Mission. (Washington, 

D.C., U.S.A.), June, 1955, pp. 281-6. 
" Operations of the Quebec Iron and Titanium Corporation." By G. G. Hatch and N. H. Coke. 

Trans. Canad. Inst. Min. and Met., 1956, 59, 359-362. 
" The Properties of High Density Concretes made with Iron Aggregate." By H. S. Davis, F. L. 

Browne and H. C. Witter. Proc. Amer. Concrete Inst., 1956, 52, 705-726. 
" The Operations of the Iron Ore Co. of Canada." By A. Choubersky. Bull. Inst. Min. Met., 

1957 (Nov.), 33-88. 
" Oxygen in Iron and Steel Making." By J. A. Charles, W. J. B. Chater and J. L. Harrison (Lond.), 

1957, 309 pp. 
" Corrosion Problems in Chemical Factories; Choice of Constructional Materials." By F. R. 

Himsworth and J. G. Hines. Chem. Age, 1957, Feb. 16th, 285-7. 
" Iron Ore Beneficiation." By L. A. Roe (111., U.S.A.), 1957, 305 pp. 



" The Manufacture of Iron and Steel." By G. R. Bashforth. Vol. 1 : Iron Production, 2nd Ed., 

1957, 306 pp. Vol. 2: Steel Production, 2nd Ed., 1959, 390 pp. 
" Production of Corrosion Resisting Steel Castings for the Uranium Industry." By G. W. 

Bousted in " Uranium in S. Africa, 1946-56," Vol. 1, 535-546. 
" Recent Advances in Metallic Materials of Construction for Use in the Chemical Industry." By 

N. P. Inglis. Chem. andlnd., 1957 (Feb. 16th), 180-9 (Corrosion Resistant Steels, 180-1). 
" Some Factors affecting the Activity of Sintered Iron Catalysts for the Fischer-Tropsch Synthes- 
is." By T. A. Dorling, D. Gall and C. C. Hall, /. App. Chem., 1958, 8, 533-549. 
" Appleby Frodingham Sinter Plants — Output and Quality Ratings." By B. L. Robertson, N. 

Haslam and R. H. Siddons. Iron and Coal Trade Rev., 1958, 176, 739-750. 
" The Pattern of Research in the Electrical Industry." By H. V. Cameron. Chem. and Jnd., 1958, 

1214-1221 (Ferrites, p. 1219). 
" Iron Ore Minerals." Ontario Research Foundation (Ontario, Canada), 1958, 212 pp. 
" The Properties of Ductile Iron." From "Gray Iron Castings Handbook," Gray Iron Founders 

Society (Cleveland, Ohio), 1958, pp. 227-270. 
" Ductile Iron combines Quality with Economy for Fluid Handling Equipment." By K. H. 

Kirgig, Ductile Iron Division, International Nickel Co. (New York), 1958, 16 pp. 
" A Survey of Modern Blast Furnace Technique." By T. P. Colclough. /. Iron and Steel Inst., 

1958,189(2), 113-124. 
" High Density Concrete for shielding Atomic Energy Plants." By H. S. Davis. Proc. Amer. 

Concrete Inst., 1958, 54, 965-977. 
" Direct Iron Ore Reduction." By P. E. Cavanagh./. Metals, 1958, 10, 804-9. 
" R. N. Direct Reduction Process." By A. Stewart and H. K. Work. /. Metals, 1958, 10, 460-4. 
*' Smelting Titaniferous Ores." By H. U. Ross. /. Metals, 1958, 10, 407-411. 
" The World's Iron Ore Supplies." By F. G. Percival. British Iron and Steel Federation, 1959, 

3rd Ed., 19 pp. 
" Iron and Steel : The Paley Report in Retrospect.' By J. D. Sullivan. Min. Engng. (New York), 

1959, 11, 789-796. 
" The Handling and Treatment of Iron Ore." Special Rep. 65, Iron and Steel Inst. (Lond.) 1959, 

128 p. 
" Economics of the Mineral Industry." Ed. by E. H. Robie, Amer. Inst. Min. Met. and Petrol, 

Engrs. (New York), 1959, 755 pp. 
" Marketing of Iron Ore." By F. G. Pardee. Ibid., 311-316. 
" Marketing of Pig Iron." By G. P. Krumlauf. Ibid., 317-318. 
" Ferro Alloys." Minerals Yearbook, U.S. Bur. Mines (Annual). 
" Iron Ore." Ibid. 
" Iron and Steel." Ibid. 
" Iron and Steel Scrap." Ibid. 
" Slag — Iron Blast Furnace." Ibid. 


The Standard Specifications for the various grades of pig iron, iron castings and 
steel issued by the British Standards Institution, the American Society for Testing 
Materials and many official bodies, are so numerous that space will not permit even 
the more important of these to be itemized here. A comprehensive sectional list of 
British Standards for Iron and Steel has been issued by the B.S.I, as P.D. 3544, 
which covers those formulated for many industrial products, aircraft material and 
components. The specifications approved by the American Society for Testing 
Materials comprise the first volume of A.S.T.M. Standards (Ferrous Metals) 
issued triennially. Other specifications issued in the United States include those 
formulated by the American Standards Association, the American Society for 
Metals, the United States Army and Navy and many Federal States. 



The chief ore of lead is the sulphide, galena (PbS) ; of less importance are the carbon- 
ate, cerussite (PbCOs), and the sulphate, anglesite (PbSCU). Lead ores most frequently 
occur associated with workable amounts of zinc blende (ZnS), and often contain 
recoverable amounts of copper, silver, gold, antimony and bismuth. Most lead-zinc 
ores as mined have to be separated and concentrated before smelting and this may 
be done by (1) wet gravity methods employing jigs and separating tables; (2) 
flotation; (3) wet gravity methods assisted by flotation, the process adopted being 
often determined by the nature of the ore. Complete separation of the lead ore from 
zinc is rarely attained by ore-dressing processes and the lead ore as sent to the 
smelter may contain, say, 75 per cent, lead, with 5 per cent. zinc. Galena, when pure, 
has a hardness of about 2-5 and a specific gravity of 7-4-7-6. It always contains 
silver in amounts from traces up to 0-25 per cent. 

World Production 

The world's production of lead ore, in terms of metal content, in 1958, totalled 
about 2,300,000 long tons, of which 594,000 long tons came from British countries. 
The countries with the largest output (in order of importance) were the U.S.S.R., 
Australia, the United States, Mexico, Canada, Peru, Morocco, Yugoslavia, S.W. 
Africa, Spain and Bulgaria. In 1958 Great Britain produced lead ore having an 
estimated metal content of 4,166 long tons and in the same year her imports 
consisted of 162,419 long tons of pig lead, 1,812 long tons of scrap and 248 long 
tons in the form of sheet and pipes. 

The world's smelter production of lead in 1958 was estimated to be about 
2,300,000 long tons, of which 388,000 were smelted in British countries. The U.K.'s 
smelter production in 1958 was about 4,000 long tons. The chief world smelters were 
the U.S.A., the U.S.S.R., Australia, Mexico, Federal Germany, Canada, Belgium, 
Yugoslavia and France. The recovery of secondary lead from old battery plates, 
etc., is an important industry in some countries, particularly in the U.S.A., where in 
1958 it amounted to 358,738 long tons. 

Smelting Lead Ores 

In general the processes in use for extracting metallic lead from its ores may be 
roughly grouped under three headings : 

(1) Roast reduction processes involving smelting the previously roasted ore in a 
blast furnace. 

(2) Air-reduction by smelting on a reverberatory furnace hearth; 

(3) Hydrometallurgical processes. 

A large proportion of the world's supply of lead is obtained by the blast furnace 
method, the other processes being employed to meet special conditions. 

In the blast furnace method, the galena is roasted so as to remove as much of its 
combined sulphur as possible. Roasting may be either (1) the ordinary sulphating 
roast at about 400-500° C, by which the sulphur content is reduced to about 



4 per cent.; (2) slag roasting in which the ore is completely fused; (3) a sintering 
roast in which the sulphides are self-burned and sintered under an air blast. 

The roasted ore is mixed with lime, iron ore, silica and fuel in such proportions 
as will reduce the lead to the metallic state and give a slag sufficiently fluid to permit 
the reduced lead to pass through it and collect at the bottom of the furnace, whence 
it is drawn off periodically. 

The crude lead so obtained may contain several per cent, of impurities, such as 
occluded slag, antimony, bismuth, copper, nickel, tin, zinc, selenium, tellurium, 
arsenic and sulphur, most of which tend to harden the metal to an undesirable 
extent. The lead also carries any silver and gold present in the ore. 

A number of methods have been devised and used on a large scale for refining 
base lead bullion. The most generally used is the Parkes process in which copper is 
first removed by melting the lead bullion, allowing it to cool below the freezing point 
of copper, which crystallizes out and is removed by skimming. The bullion then 
passes to a reverberatory, or softening, furnace where the temperature is raised and 
the metal drossed by a blast of air, which causes the oxidized antimony and arsenic 
to rise as a dross, which is skimmed off. The lead is next treated to remove silver and 
gold by adding to the molten metal small quantities of zinc in which the precious 
metals are more soluble than they are in lead, and so become concentrated in the 
zinc which, being lighter than the lead, rises to the surface and is skimmed off. The 
refined lead is cast into pigs. In the Pattinson process, which is no longer generally 
used, when the lead is cooled very slowly part of it will solidify and can be skimmed 
off, the silver remaining in the molten portion. The Betts process, used in several 
plants in the U.S.A., is electrolytic and suitable for treating lead bullion high in 
bismuth. The Betterton process for the removal of bismuth is fire-refining by a 
liquation process applied to soften and desilverize lead. Normally a calcium- 
magnesium alloy is used to combine with the bismuth to form a solid compound, 
which separates out. A new electrolytic refining process now being used in Italy 
involves the use of a sulphamate electrolyte for the removal of tin and bismuth. 


The largest use for lead in Great Britain is for coverings for electric cables, but 
in the United States the biggest demand is for making plates for electric storage 
batteries. Large quantities of lead are also used in both countries in building, for 
water pipes, roofing, etc. 

Metallic lead is the principal constituent of many industrial alloys, such as anti- 
friction, babbit, magnolia and white metals; die castings and type metal. It is also an 
essential component of many solders, fusible alloys, brasses and bronzes, and lead 
foil, which is extensively used for wrappings. Terne plates, which are steel plates 
coated with an alloy of lead and tin, are normally used in Great Britain for packing 
dry goods and in the United States for roofing. 

Lead is of interest to the chemical and allied industries chiefly on account of the 
use of chemical lead for the manufacture of plant required to resist corrosion : in 
electric storage battery plates and as the starting point in the manufacture of such 
compounds as white lead, basic sulphate of lead, red and orange lead, lead chromate, 



zinc-lead white, litharge and red lead for pasting on accumulator plates and in glass- 
making. Occasionally, galena is used direct in the manufacture of some lead pigments 
such as basic sulphate of lead. 

The consumption of lead in the United States by the principal industries is 
shown in Table 86. 

Table 86 

Consumption of Lead by Industries in the United States* 

Short tons 






Metal products . 

Storage batteries 

Pigments .... 














Total .... 






* From " Minerals Yearbook ", U.S. Bur. Mines. 

t Excludes 42,056 short tons of lead, which went directly from scrap to fabricated 
products and 8,224 short tons of lead contained in lead-zinc oxide and other unspecified 

^Excludes 35,883 short tons of lead, which went directly from scrap to fabricated 
products, and 5,141 short tons of lead contained in lead-zinc oxide and other unspecified 

Table 87 

United Kingdom Consumption of Lead by Uses* 

Long tons 





Cables ..... 

Batteries — as metal 

Battery oxidest 

Tetraethyl lead 

Other oxides & compounds 

White lead . . . . 

Shot (including bullet rod) 

Sheet and pipe 

Foil and collapsible tubes 

Other rolled & extruded . 

Solder .... 

Alloys ..... 






















































Total consumption . 






* From Bulletin British Bureau of Non-ferrous Metal Statistics, Birmingham, England. 

t Mainly grey oxide. 



The consumption of lead in Great Britain in 1956-9 is shown, by industries, in 
Table 87. 


Cable Sheathing. Large quantities of lead are used in the manufacture of sheath- 
ing for electric cables and the requirements of British Standard Specification 
B.S. 801 : 1953 as regards chemical composition are shown in Table 88. 

The metal described in the table in column (1) is considered suitable for use 
where a high degree of pliability is the primary consideration; otherwise, alloys B, 
or E are usually more suitable owing to their higher fatigue resistance. Alloy E has 
less resistance to fatigue than alloy B, but is still adequate for all but the most 
severe conditions of service. 

Table 88 

Lead for Cable Sheathing, B.S.I. Specification B.S. 801 : 1953 




Lead cable 

Lead alloy 

Lead alloy 








Alloy B 

Alloy E 

Lead, min. .... 




Tin, max. .... 




Antimony, max. . 



0-1 5-0-25 

Cadmium, max. . 


Zinc, max. .... 


Bismuth, max. 


Other impurities, including 

bismuth and zinc, max. 



* If the lead is to be used unalloyed and the purity is higher than 
99-995 per cent., a small addition of tin or antimony may be made to 
ensure satisfactory working and service. 

Storage Batteries. The lead plates of electrical storage batteries often consist of 
perforated grids of an alloy of lead with 5-12 per cent, of antimony and occasionally 
up to 0-25 per cent, of tin. The negative plates have their interstices filled with a 
paste which may consist of litharge, or a mixture of 75 per cent, litharge with 25 per 
cent, red lead. The paste on the positive plate usually contains a larger proportion 
of red lead, up to 50 per cent. Alternatively, a grey oxide paste may be used. This 
consists of partially oxidized metallic lead particles formed by a combined grinding 
and oxidizing process in a ball mill. The grey oxide normally contains about 60 
per cent, of metallic lead particles, which after the electrical treatment usually in- 
volved in battery production, are converted to negative spongy lead and positive 
lead dioxide. It is stated that in 1957 battery makers in the United States produced 
over 100,000 tons of black-grey suboxide of lead for their own use. 

Regulus Metal. Lead may be hardened by additions of antimony, which, how- 
ever, should contain only traces of arsenic or zinc — usually less than 01 per cent. 



of the regulus alloy produced. The tensile strength and hardness of the regulus 
metal increases with the antimony content, and alloys containing 6-8 per cent, of 
antimony may be used for parts of plant required to have greater strength and rigidity 
than that of chemical lead, but not subject to considerable abrasion. Lead carrying 
8-10 per cent, antimony may be used for valves, cocks, etc., required to withstand 
abrasion. Higher percentages may be used, though rarely over 12 per cent. 

B.S.I. Specification 335 : 1928 for regulus metal provides for four grades of 
metal based on antimony percentages of 6-8, 8-10, 10-12, and over 12, the balance 
in each case being lead. In each grade the maximum permissible quantities of arsenic 
and zinc are limited to 001 per cent, each and of copper and tin to 010 per cent, 
each. Sulphur must not exceed 02 per cent. The minimum ultimate tensile strength 
of the four grades is 6,000, 7,000, 8,000 and 9,000 lb. per sq. in. respectively and the 
minimum for Brinell hardness is 15, 16, 17, and 19 respectively. 

Chemical Lead. Pipes, sheets and castings of lead are used in the construction of 
plant which will be subjected to corrosive action, such as in sulphuric acid chambers. 
A tendency to use special alloys containing small amounts of added metals, such as 
copper, tellurium and nickel, to improve the physical properties continues. Hard, or 
regulus, lead is often used for vessels, pans, frames and other constructional units, as 
it has greater mechanical strength, although its resistance to corrosion is less than 
that of pure lead. 

Specifications for chemical lead have been formulated in several countries, and 
some of these are summarized in Tables 89 and 90. B.S. 334 : 1934 has been adopted 
by the Standards Association of the Union of South Africa. 

Table 89 

British Standard Specification for Chemical Lead: B.S. 334 : 1934 



B.S. 334 

Type A »f 



(fine grain) 

B.S. 334 




(fine grain) 

B.S. 334 

Chemical lead 

(fine grain) 
B.S./S.T.A. 7f§ 

Metallic Lead, min. 





Copper, max. 





Antimony, max. . 





Bismuth, max. 





Iron, max. .... 





Nickel and Cobalt, max. 





Silver, max. .... 





Zinc, max. .... 





Tellurium, max. . 





Tin, Cadmium, Arsenic, 

Sulphur, max. . 





Total of all impurities, max. . 


* Identical with B.S./S.T.A.7 Schedule of Service Non-ferrous Metals and Alloys 
Specification, 1944. 

t Has also to comply with B.S.I. Flash and Aqua Regia tests. 

% Has also to comply with B.S.I. Flash test. 

§ Type A Chemical Lead has to be used in the manufacture of this material. 



In the flash test referred to in Table 89, a prepared specimen of the lead is 
heated in a 95-96 per cent, solution of pure sulphuric acid. The rate of heating is 
controlled so that a temperature of 300° C. is reached in seven minutes. The bulb 
of the thermometer, inserted in a cavity in the specimen, should not become ob- 
scured with a deposit of lead sulphate until a temperature of 285° C. has been reached. 
In special cases a minimum temperature limit of 300° C. may be specified. 

The aqua regia test consists in slowly heating a piece of the lead in a specified 
aqua regia solution for thirteen minutes until a temperature of 109° C. is reached. 
Temperature is maintained at this point for a further seven minutes. The time which 
is taken for spots of lead chloride to appear on the metal is noted and also that at 
which vigorous action starts. 

From the results of this test the grade of the lead is assessed as indicated in 
Table 90. 

Table 90 

Aqua Regia Test for Chemical Lead: B.S. 334 


Quality of Lead 

of lead 

action starts 

Appearance of sample at end of test 

Very good 





Under 12 

None at 20 

»> »» >> 

Started after 

Less than 18 

No pitting or uneven attack. 
Slight pitting, but no uneven attack. 
No deep pitting, only slight uneven 

Heavy and deep pitting, vigorous and 

uneven attack, visible reduction of 


The notes attached to the S.T.A. 7 specification give some useful suggestions 
regarding the suitability of the various grades of chemical lead dealt with in Table 
89. Type A should only be used where the highest degree of corrosion resistance is 
required, as the large and variable grain size which may occur in the metal may 
render it liable to develop intercrystalline cracking if it is subjected to certain 
conditions of stress, such as vibration or repeated variations in temperature. 

Fine grain chemical leads have high resistance to corrosion, which, for most 
purposes, is not noticeably inferior to that of Type A. Its refined grain size gives the 
material improved mechanical properties which make it suitable for conditions 
where vibration or thermal expansion and contraction are likely to occur. Copper 
chemical lead (fine grain) is recommended for general chemical purposes, as its 
resistance to corrosion is generally adequate. Copper-tellurium lead (fine grain) is 
a specially tough fine grain alloy with a high fatigue resistance and a corrosion 
resistance about equal to that of copper chemical lead, but it is harder to work. It is 
stated to be particularly suitable for use under conditions involving severe vibration. 

Specification H/10 of 1938 for chemical lead, issued by the Australian Common- 
wealth Engineering Standards Association, has the same requirements as regards 
chemical composition of Grade A as B.S. 334, except that the permissible limit for 
antimony is raised to 0004 per cent, and the flash and aqua regia tests are omitted. 



For Grade B chemical lead, containing alloying elements, the composition is a 
matter for agreement between buyer and seller, but in other respects it has to con- 
form to those specified for Grade A lead. 

The U.S. National Stockpile Specification P-28-R of August 5th, 1952, covers 
the following grades of pig lead: corroding lead, common desilverized lead, soft 
undesilverized lead and chemical lead. It requires that all grades of pig lead shall 
conform to the chemical requirements of the A.S.T.M. B29, latest revision. 

A.S.T.M. Specification No. B 29-55 for pig lead covers refined lead in pig form 
made from ore, or other material, by processes of reduction and refining, but not 
reclaimed lead which is a commercial product obtained by the recovery of metallic 
lead and its alloys by the simple reclaiming process of melting, drossing and casting. 
The various types of pig lead covered by this specification are: corroding lead, 
chemical lead, acid-copper lead and common desilverized lead. The several types 
of lead shall conform to the requirements as to chemical composition as shown in 
Table 91. 

Table 91 

Pig Lead. A.S.T.M. Specification B 29-55 







Per cent. 

Per cent. 

Per cent. 

Per cent. 

Silver, Ag, max. .... 





„ „ min. .... 





Copper Cu, max 





„ „ min 





Silver and Copper together Ag + Cu, 






Arsenic and Antimony, and Tin, As + 

Sb + Sn, max. .... 





Zinc, Zn, max 





Iron, Fe, max. ..... 





Bismuth, Bi, max. .... 





Lead, Pb, by difference, min. 





Note: Corroding lead is a designation that has been used in the trade for many years to 
describe lead which has been refined to a high degree of purity. Chemical lead is used in the 
trade to describe the undesilverized lead produced from South-eastern Missouri ores. 
Acid-copper lead is made by adding copper to fully refined lead. Common desilverized lead 
is a designation used to describe fully refined desilverized lead. 

The U.S. Federal Standard Specification QQ-L-171 of June 23rd, 1931, requires 
that grade A lead for foundry use shall contain a minimum of 99-9 per cent, lead, 
and grade B lead for use as weights or ballasts, etc., shall contain a minimum of 
95 -0 per cent. lead. 

Lead intended for use in the manufacture of tetraethyl lead must have a high 
degree of purity, particularly in regard to bismuth, which should not exceed 0-01 
per cent. 

Metallic lead has an important use as a biological shield against the harmful 



effect of gamma radiation, which may be emitted by various products in the atomic 
pile. The best protection is given by high density metals, such as lead, gold, mercury, 
etc., and the cheapest and most easily fabricated is lead. The metal is used in the 
form of either bricks or sheets of the metal, or as blocks or shields of glass con- 
taining 60 per cent, lead oxide. Such glass has a density of 4-3, as compared with 
about 2-7 for ordinary glass. One special type of heavy glass has a density of 6-1 
and contains 80 per cent, of lead oxide. 

Lead when used for shielding purposes does not become contaminated and may 
be used continuously without becoming radioactive and emitting harmful rays. 
It must therefore be free from most impurities. Atomic reactors operated by the 
U.S. Atomic Energy Commission employ a combination of concrete, lead, cadmium 
and space to protect operating personnel from all types of radiation, including 
alpha, beta, gamma and neutron rays. 

Lead Powder is finding a number of uses in industry, such as in leaded paints or 
sprays for protective applications, in the production of free-cutting steels, in heavy 
leaded resins as a protective coating for radioactive metal containers and in storage 
batteries. The percentage composition of typical samples of " Atomet " lead powder 
made by Durham Chemicals Ltd., of Birtley, Co. Durham, is as follows: lead, Pb, 
99-5; iron, Fe, 005; bismuth, Bi, 01 ; copper, Cu, 0001 ; zinc, Zn, 0002; antimony, 
Sb, 0-005; moisture, 05; oxide, trace. 

The physical properties of the three grades marketed are as follows: 

100/ dust 



Surface area (cm. 2 /gm.) 

. 286 



Mean equivalent spherical particle 


(microns) ..... 

. 18-5 



Sieve test: 

Retained on 100 B.S. sieve 

. nil 



Passing 300 B.S. sieve (per cent.) 

. 75 



Packing density (lb./cu. ft.) 

. 400 



Specific gravity .... 

. 113 




The chief lead pigments are white lead, red lead, calcium plumbate, basic 
sulphate of lead, leaded-zinc white, powdered and flake lead and the lead chromates. 
Litharge is not a paint pigment, as such, but is employed in the industry as a 
starting material, in addition to its other uses. 

The starting point for the manufacture of most lead pigments is usually pig 
lead, although sometimes high-grade ore (galena) is used. In Great Britain and the 
United States pig lead is used almost exclusively, directly or indirectly, in the manu- 
facture of white lead, litharge, red lead and orange lead. It is also used in those 
countries for making basic lead sulphate pigment, though galena provides raw 
material for about half the output of each. 



White lead is a basic carbonate of lead, approximating to the formula 2PbC03. 
Pb(OH)2, but its composition varies considerably according to the method of 

The production of the best quality basic carbonate white lead pigment requires 
the use of high-grade metal, usually described as " corroding lead." 

The presence in the lead of small amounts of copper or antimony gives the finished 
white lead a greyish tint and small amounts of silver may cause a pinkish discolora- 
tion. Bismuth also tends to give greyish tints and its presence is usually not tolerated 
in amounts over 05 per cent, of the lead. About 90 per cent, of the white lead 
manufactured is used in paints, and possibly 3 per cent, in ceramic products. 

B.S. Specification B.S. 239 : 1952 for genuine white lead for use in paint requires 
the material, after drying at 98-102° C, to contain not less than 99 per cent, of 
hydroxycarbonate of lead, which latter shall consist of not less than 20 per cent., 
or more than 37 per cent., of lead hydroxide chemically combined with not more 
than 80 per cent., or less than 63 per cent., of normal carbonate of lead. The matter 
volatile at 98-102° C. must not exceed 0-5 per cent, and coarse particles not passing 
a 240-mesh sieve must not exceed 0-3 per cent. The dry pigment should have an oil 
absorption, as determined by the specified method, of not less than 7 or more than 
13. Water soluble matter must not exceed 0-5 per cent, and the alkalinity of the 
water extract, calculated as Na2C03, must not exceed 01 per cent, of the pigment. 
This specification has also been adopted by the Standards Associations of New 
Zealand and of the Union of South Africa. 

A.S.T.M. Specification D 81-43 for white lead basic carbonate requires the 
material to be free from adulterants and to contain only traces of such impurities as 
are incidental to the well-controlled manufacture of high-grade basic carbonate of 
lead. The percentage of lead carbonate must be between 62 and 75, moisture and 
other volatile matter must not exceed 0-7 per cent., and the total of all other 
impurities is limited to 1 per cent. Coarse particles not passing a 325-mesh sieve 
must not exceed 1 per cent. 

Basic carbonate white lead according to Specification S.A.B. S.36-1948, of the 
South African Bureau of Standards, should contain between 67 and 75 per cent, 
of lead carbonate and the total of lead hydroxide and lead carbonate should be not 
less than 99 per cent. Acetates present, expressed as acetic acid, should not 
exceed 0-35 per cent. The total impurities including moisture and water soluble 
matter should not exceed 1 per cent., the moisture being limited to 0-5 per cent, and 
matter soluble in water to 0-5 per cent. Alkalinity expressed as ml of 01 N hydro- 
chloric acid must not exceed 20- 1. The oil absorption should be between 8 and 15 
and the residue remaining on an A.S.T.M. 325-mesh sieve should not exceed 1 per 

Specification K 9-1940 of the Australian Commonwealth Engineering Standards 
Association requires genuine dry white lead to contain from 25 to 33 per cent, of 
lead hydroxide chemically combined with not more than 75 per cent, or less than 67 
per cent, of normal carbonate of lead. Water soluble matter is limited to 0-5 per 
cent., and loss at 98-102° C. to 0-5 per cent. Acetates, calculated as acetic acid, must 
not exceed 015 per cent, and the total impurities, including moisture, must not 



exceed 1 -5 per cent. Coarse particles not passing B.S.I. 240-mesh sieve are limited to 
0-75 per cent. The reducing power of the pigment has to equal that of a standard 
sample supplied by the purchaser. 

White Basic Sulphate of Lead. This is a standard white pigment in the United 
States and approximates to the formula PbO.PbS04. It is usually made, either by 
vaporizing high grade galena at a high temperature in the presence of air, or by 
spraying molten lead into a jet of ignited fuel gas and air in a special furnace into 
which sulphur dioxide is also introduced. A typical analysis of high grade galena 
suitable for use in making this pigment is as follows: lead, 80 per cent.; zinc, 2-5 
per cent. ; silica, 2 -4 per cent. ; moisture, 6 • 1 per cent. ; silver, 5 oz. per ton. 

It is usually not such a good white colour as high-grade basic carbonate white 
lead, but it is claimed to be more stable in colour when used in exterior paints in 
cities where it is subject to sulphurous gases. 

A variety of basic sulphate of lead collected from the fumes arising from lead 
smelting has a bluish colour due to the presence of small amounts of sulphide of 
lead and carbon. It is known in the United States as " blue lead basic sulphate " and 
is stated to be useful for coating metallic surfaces. 

B.S.I. Specification B.S. 637 : 1952 requires basic sulphate of lead for use in 
paint to contain not less than 15 per cent, or more than 28 per cent, of lead monoxide 
chemically combined with not more than 85 per cent, or less than 72 per cent, of 
normal sulphate of lead, so as to constitute together not less than 94 per cent, of the 
pigment. Zinc oxide must not exceed 5 per cent, and other impurities must not be 
over 1 per cent. The proportion of zinc oxide may be varied by agreement between 
buyer and seller. The proportion of lead monoxide may also be varied by agree- 
ment. Coarse particles not passing a 240-mesh B.S.I, sieve must not exceed 01 per 
cent. ; volatile matter at 98-102° C. is limited to a maximum of 0-7 per cent, and the 
water-soluble matter to 1 per cent. The water-soluble extract must be neutral to 
methyl red. 

A.S.T.M. Specification D 82-44 for basic sulphate white lead requires that the 
pigment shall contain lead oxide, 15-28 per cent., the remainder, excluding impuri- 
ties, being lead sulphate. Zinc oxide is limited to 5 per cent. The total of other im- 
purities, including moisture and other volatile matter, must not exceed 1 per cent, 
and coarse particles not passing a 325-mesh sieve must not exceed 1 per cent. 

Most of the basic lead sulphate produced in the United States for use as a pig- 
ment is made from ore mined near Joplin, Missouri, and contains very little zinc 

Blue-lead basic sulphate according to A.S.T.M. Specification D 405^tl must 
have a composition within the following limits: lead sulphate, minimum 45 per 
cent. ; lead oxide, minimum 30 per cent. ; lead sulphide, maximum 12 per cent. ; lead 
sulphate, maximum 5 per cent.; zinc oxide, maximum 5 per cent.; carbon and 
undetermined matter, maximum 5 per cent.; and coarse particles retained on 
325-mesh sieve, maximum 1 per cent. 

Leaded Zinc Oxide. This pigment, which finds extensive use in the United 
States, and to a smaller extent in Great Britain, is dealt with under " Zinc " 
(see p. 723). 



Red Lead. This pigment is produced by the oxidation of lead, first to the monoxide 
PbO, and then to red lead PD3O4. The oxidation of the lead is said to be accelerated 
by the addition of traces of antimony. The lead is first drossed at about 340° C. in a 
pot or furnace and the monoxide so formed is oxidized in a hand or mechanical 
furnace at a temperature not exceeding 460° C. Modern practice favours the mechani- 
cal furnace. 

The proportion of true red lead, Pb304, in the final product may be varied at 
will: the higher ranges, over 9315 per cent. Pb 3 4 , do not set with linseed oil and 
are suitable for use in ready-mixed paints. 

The analyses of well-known brands of commercial refined pig leads suitable for 
manufacture of red lead and litharge are given in Table 92. 

Table 92 

Pig Lead for Red Lead or Litharge 



Per cent. 

Per cent. 

Copper .... 









Silver . 






Arsenic . 



Zinc (less than) 






About 60 per cent, of the world production of red lead is used in pasting the 
plates of electric storage batteries, whilst about 30 per cent, is used in paint, mostly 
for protecting iron and steel. Other uses include its employment in the manufacture 
of flint and optical glass, in some pottery glazes, match-making, jointing com- 
positions and in the manufacture of driers for oil varnishes. 

B.S.I. Specification 217 : 1952 for red lead for use in paints and jointing 
compounds, which has also been adopted by the New Zealand Standards 
Association, recognizes three types: (a) ordinary red lead for paints; (b) red lead for 
jointing purposes ; and (c) red lead (non-setting). It requires the following percentage 
compositions : 

(a) Pb 3 04, min. 72 equivalent to Pb0 2 25 1 
*(*) ,. „ 43 „ „ „ 15 

(c) „ „ 93 15 „ „ „ 32-5 

* A maximum of 72 per cent. Pb3C>4 is fixed for type (b). 

For type (c) a test for non-setting properties is specified. 

In types (a) and (b) the particles not passing a 100-mesh sieve must not exceed 
0-5 per cent., with a limit of 1 -5 per cent, for those retained on a 240-mesh sieve. In 
type (c) matter retained on a 100-mesh sieve must not exceed 0-1 per cent., and on a 
240-mesh sieve, must not exceed 0-75 per cent.: volatile matter at 98-102°C. is 



limited to 0-2 per cent., and the water-soluble matter to 0-3 per cent. Oil absorption 
should be between 4 and 10, or such figures as may be agreed between seller and 

The Australian Commonwealth Engineering Standards Association Specifica- 
tion K 19 of 1941, for genuine red lead (dry) for use as a pigment, requires a 
minimum content of 99 per cent, of lead oxide, of which 72 per cent, must be true 
red lead (PbsCH), for setting varieties and 93 per cent, in the non-setting type. The 
pigment must be free from organic colouring matter and its content of water- 
soluble matter must not exceed 0-5 per cent. The loss at 95-98° C. is limited to a 
maximum of 0-5 per cent, in setting varieties and to 0-2 per cent, in non-setting red 
lead. Coarse particles not passing a 100-mesh sieve (I.M.M.) must not exceed 0-5 
per cent., and those retained on a 200-mesh sieve (I.M.M.) are limited to 1 -5 per 

Specification l-GP-14-1946 of the Canadian Government Purchasing Standards 
Committee requires red lead for use in paints to contain not less than 95 per cent, of 
Pb304 and that the total moisture, water-soluble matter and matter insoluble in a 
mixture of nitric acid and hydrogen peroxide shall not exceed 1 per cent. Coarse 
particles retained on a 325-mesh sieve (44 microns) must not exceed 1 per cent. 

A.S.T.M. Specification D 83-41 recognizes three grades of red lead (for use in 
paint) containing respectively 85, 95 and 97 per cent, of Pbs04, the remainder being 
PbO. The total impurities, including moisture, water-soluble matter and matter 
insoluble in a mixture of nitric acid and hydrogen peroxide, must not exceed 1 per 
cent. When mixed with specified quantities of linseed oil, driers and turpentine, and 
brushed out on a smooth vertical iron surface, the paint must dry hard and elastic 
without running, streaking or sagging. 

Calcium Plumbate. This compound, which has the formula 2CaO.Pb02, was 
first employed to any extent as a pigment in priming paints about the middle of 
World War II as a means for economizing the use of lead. When made into paint 
with linseed oil it was found to have rust inhibiting properties of the same order as 
red lead. 

The production of the pigment on a commercial scale was started by Associated 
Lead Manufacturers Ltd., London, in 1950, and has been continued since on an 
increasing scale. The pigment is cream-light stone in colour, has a sp. gr. of 5-7; 
oil absorption, 12-15 per cent.; opacity about twice that of white lead, and a loose 
bulking weight of 12-4 gm./cu. in. Calcium plumbate paints in linseed oil are very 
resistant to attack by sea-water and are claimed to be unique in their good adhesion 
to new galvanized iron and steel without any prior treatment of the surface. They 
are being extensively used in primer paints for the protection of water-sealed gas- 
holders from corrosion. Specifications for calcium plumbate pigments and paints 
have been formulated by the Ministry of Supply. 

Orange Lead. Sometimes called orange mineral, this is a variety of red lead 
produced by the calcination of white lead. It contains upwards of 95 per cent, true 
red lead, has a low bulk density and less tendency than has ordinary red lead to set 
in paint media containing varnish. It is valuable as a pigment for printing inks, and 
is used to a small extent in certain enamels and lakes. 



Flake Metallic Lead. This material is prepared by atomizing metallic lead and 
then " flaking " the product in a ball mill in the presence of mineral spirit and 
stearic acid. The action of the ball mill is to flatten out the particles of lead into thin 

The chief use for flake metallic lead is as the sole pigment in paints used as 
primers for treating galvanized iron, stainless steel, aluminium and magnesium 
articles. Its preservative action differs from flake aluminium in that it mostly sinks 
to the bottom of the paint film, whereas the aluminium largely floats. 

Lead Chromate. The lead chromes, an important group of yellow and orange 
pigments have already been considered under " Chromium " (see p. 128). 

Other Uses 

Tetraethyl lead, Pb(C 2 6 ) 4 , a heavy liquid produced by reacting a lead-sodium 
alloy with ethyl chloride, is used extensively as an addition to motor and aviation 
petrol to increase its octane number. About 2 to 4 cc. is added to each gallon of 
premium petrol and up to 1 -5 cc. to most other petrols. The demand for tetraethyl 
lead has not kept pace with the demand for high octane petrol, owing to the 
increased production of reformed petrol, which has some inherent antiknock 

Litharge. This compound is used principally in filling the grids of electrical 
storage battery plates, in flint glass, in making frits for earthenware glazes, for the 
production of lead acetate and nitrate, for driers for paint and varnish, in proofing 
fabrics, in the manufacture of certain rubber goods, linoleum, lead plaster and in 
some insecticides. 

The best qualities contain as little as 05 per cent, of matter insoluble in acetic 
acid and are practically free from grit, metallic lead and lead peroxide. 

For use in glass manufacture, litharge should contain only small traces of iron, 
copper and silver. 

Of the 131,525 short tons of litharge used by industry in the United States in 
1956, about 63 per cent, was used in storage batteries, 15 per cent, in ceramics, 
2-7 per cent, in the manufacture of lead chrome pigments, 2-7 per cent, in oil 
refining, 2-7 per cent, in varnish making, with smaller amounts in the manufacture 
of rubber, insecticides and floor coverings, etc. 

Other lead compounds have a number of industrial uses in addition to those 
mentioned above. Lead borate, linoleate, tungate, stearate, oleate and resinate are 
used as driers in paints and varnishes; lead acetate is used in making chrome yellow, 
as a mordant in dyeing and for impregnating certain damp-resisting fabrics; lead 
arsenate is extensively used in horticultural insecticides and sheep dips; lead nitrate 
in dyeing and calico printing, match heads and pyrotechnics; lead phosphate for 
weighting silk. Sodium plumbite, NaPb(OH>3, is used in refining mineral oil under 
the name of " Doctor solution." 

Lead metaniobate, an unusual new high-temperature material, is stated to have 
possible applications in guided missiles. It is a piezoelectric material which gives off 
small voltages when acted upon by outside physical forces, such as vibration. It is 
stated to retain most of its properties up to a temperature of about 500° C. 

l2 291 


Lead azide, Pb(N3)2, is a powerful initiating explosive which has found use, 
since about 1893, as a substitute for mercury fulminate. 

Certain binary lead compounds are semi-conductors claimed to have unusual 
properties. Lead telluride, selenide and sulphide crystals have infra-red detection 
properties. Lead sulphide is now an essential component of a system developed for 
the U.S. Army's Nike-cajun rocket used to measure the water vapour content of the 
earth's gaseous envelope. Lead sulphide photoconductive cells in combination with 
infra-red light form part of another process for recording an optical-magnetic 
soundtrack on motion picture films. 


" Metallurgy of Lead." By H. O. Hofman. New York, 1918. 664 pp. 

" Lead: Its Occurrences in Nature, Modes of Extraction, Properties and Uses." By J. A. Smythe. 

(Lond.), 1923, 343 pp. 
" Red Lead for the Glassmaker." By R. L. Hallows. Glass Ind., 1928, 9, 269-71. 
" Materials for Chemical Plant Construction." Part III. " Lead." By A. H. Loveless, lndustr. 

Chem., 1932, 8, 289-90, 310-12 and 352-3. 
" Description of continuous Lead Refining at the Works of the Broken Hill Associated Smelters 

Proprietary Ltd., Port Pirie, South Australia." By G. K. Williams. Proc. Aust. Inst. Min. 

Metal., 1932, No. 87, 75-177. 
" Lead." Anon. Min. Indus. Br. Empire and Foreign Countries, Imperial Institute, (Lond.), 1933, 

253 pp., including bibliography. 
" Red Lead Paints (1930-1935)." Science Library Bibliogr. Ser. No. 198, (Lond.), 1935 (102 

" Flaked Metallic Lead." By F. J. Licata. " Protective and Decorative Coatings." Ed. by J. J. 

Mattiello, Lond. and New York, 1942, Vol. 2, pp. 603-10, including bibliography. 
" Lead Pigments." By C. H. Rose. Ibid., pp. 327-68, including bibliography. 
" Smelting Battery Scrap." By C. R. Hayward. Metal Ind., 1944, 65, 228. 
" Lead." By R. J. Bowman. " Handbook of Non-ferrous Metallurgy." Ed. by D. M. Liddell, 

(Lond.), 1945, pp. 144-215. 
" Electrolytic Refining of Lead." By G. Reinberg. " Handbook of Non-ferrous Metallurgy." 

Ed. by D. M. Liddell, (Lond.), 1945, Vol. 2, pp. 370-8. 
" Smelting at Port Pirie, South Australia." By A. T. Armstrong. S. Aust. Dep. Mines Min. Rev., 

No. 85, 1946, pp. 110-33. 
" The Chemist in the Storage Battery Industry." By M. Barak. Chem. and Ind., 1949, pp. 444-7. 
" Outlines of Paint Technology." By N. Heaton. 3rd Ed. (Lond.), 1949, 448 pp. (Lead pigments, 

pp. 54-69, 114-17). 
" The Refining of Lead and Associated Metals at Port Pirie, South Australia." By F. A. Green. 

" The Refining of Non-ferrous Metals," Inst. Min. Met. (Lond.), 1949, pp. 281-316. 
" Lead in Modern Industry." Lead Industries Association, New York, 1952, 230 pp. 
" An Integrated Plant for Tetraethyl Lead." Indus. Chem., 1954, Sept., pp. 429-436. 
" G.E. Pilot Output of New Lead Material." [Lead Metaniobate.] American Metal Market, 1956, 

63, No. 175, 12. 
" Betterments of the Quality of Refined Lead." By J. S. Jacobi and B. H. Wadia. Bull. Inst. Min. 

Met., (Lond.), 1958, 67, 141-61. 
" Lead Compound Semi-Conductors." Lead, Lead Industries Association, New York, 1958, 22, 

No. 1, 5. 
" Lead Based Paints in Corrosion Control." By N. J. Read, /. Oil and Col. Chem. Ass. (Lond.), 

" Lead." By O. M. Bishop. " Mineral Facts and Problems." U.S. Bur. Mines Bull. 585, 1960, 

16 pp. 
" Lead as a Corrosion Resistant Material." Lead Development Association. (Lond.), 6 pp. 
*' Calcium Plumbate, A Pigment of Growing Importance." Lead, Lead Development Association, 

(Lond.), 1959. 
" Lead." U.S. Bur. Mines, Minerals Yearbook. (Annual) 
" Lead and Zinc Pigments and Zinc Salts." U.S. Bur. Mines, Minerals Yearbook. (Annual) 

Standard Specifications 

American Society for Testing Materials 
A.S.T.M. Standards, 1958: 

Basic Sulphate White Lead for use in Paints. D 82-44 

Basic Carbonate White Lead „ „ D 81-43. 

Blue Lead (basic sulphate) „ „ D 405-41. 



Leaded Zinc Oxide for use in paints. D 80-41. 

Red Lead Pigment „ „ D 83-41. 

Lead Titanate Pigment. D 606-42. 

Pig Lead. B 29-55. 
Australian Commonwealth Engineering Standards Association 

Chemical Lead. H 10, 1938. 

Red Lead. K 19, 1941. 

White Lead. K 9, 1941. 
British Standards Institution 

Basic Sulphate of Lead. B.S. 637 : 1952. 

Chemical Lead (Types A & B). B.S. 334 : 1934. 

Lead and Lead Alloys for Cable Sheathing. B.S. 801 : 1953. 

Lead Regulus. B.S. 335 : 1928. 

Red Lead for Paints and Jointing Compounds. B.S. 217 : 1952. 

Genuine White Lead for Paints. B.S. 239 : 1952. 
Canadian Government Purchasing Standards Committee 

Red lead for use in Paints l-GP-14-1946. 
South African Bureau of Standards 

Basic Carbonate White Lead. S.A.B.S. 36-1948. 

U.K. Ministry of Supply, Lond. 

Calcium Plumbate Pigment and Paint, No. 3032 and 3035. 

U. S. Federal Specification 

Lead for Foundry Use. QQ-L-171, June 23rd, 1931. 
U.S. National Stockpile Specification 

Pig Lead. P-28-R, August 5th, 1952. 

Limestone, Chalk and Whiting 

Minerals in which the principal constituent is the mineral calcite (calcium carbonate) 
appear in trade under the designations of Iceland spar, limestone, marble, chalk and 
whiting. The name limestone is applied, often rather loosely, to any stratified rocks 
chiefly composed of either calcium carbonate, the double carbonate of calcium and 
magnesium, or mixtures of these two products. Limestones carrying 5-20 per cent. 
MgO are usually called magnesian limestones, whilst those with over 20 per cent, 
are known as dolomites. The use of dolomite as a refractory and for the production 
of metallic magnesium and its compounds is dealt with under " Magnesium." 
Marble is a variety of limestone in which the carbonates have recrystallized into a 
dense form which can be polished. Chalk is a fine-grained friable limestone com- 
posed of microscopic remains of marine organisms. Whiting can be either finely 
ground calcium carbonate prepared from chalk, marble or limestone, or the product 
obtained by chemical precipitation from a solution or suspension containing lime. 
In some localities where limestone is not economically available, calcined sea 
shells are sometimes used as a source of lime, or for the manufacture of Portland 
cement. Thus, oyster shells from the oyster canning industry are so used in Balti- 
more, U.S.A., and other sea shells have been similarly employed in Holland and 
West Africa and even in Cornwall, England, during World War II. Lime made from 
shells dredged from Galveston Bay was used on a large scale during the war in the 
extraction of magnesium from sea-water at Freeport, Texas, U.S.A., the shells, 



after washing, being calcined in rotary kilns by natural gas. Shell sold or used by 
producers in the U.S.A. in 1958 totalled nearly 19 million short tons. 

In India and elsewhere a considerable amount of lime, chiefly used for plastering, 
is made by burning an impure calcium carbonate, known as kunkur, which occurs 
in lumps in surface soils. 

Although for some purposes the three most commonly occurring forms of 
natural calcium carbonate, i.e. limestone, marble and whiting, are interchangeable, 
there are a number of uses where the physical condition of the material determines 
its suitability for a specific purpose. For this reason, it will be convenient to deal 
separately with (1) limestone and, (2) whiting. 


When pure, this mineral consists of carbonate of lime (CaCOs), but such material 
is rarely found except in the form of crystalline calcite, which has specific gravity 
about 2-7 and hardness about 3. Commercial limestones always contain variable 
amounts of iron oxide, alumina, magnesia, silica, phosphorus and sulphur. The 
content of lime (CaO) may vary between 22 and 56 per cent., magnesia (MgO) from 
nil to 21 per cent. Alumina (AI2O3) is usually fairly low, but argillaceous limestones 
may carry over 5 per cent. Iron oxides rarely exceed 3 or 4 per cent. Silica may be 
present either in the form of quartz or as a constituent of clay. 

Limestone, either as such or after calcination to lime, has many uses in chemical 
industry, such as in the manufacture of lime, Portland cement, alkali, glass, paper, 
calcium carbide, in sugar refining, as a flux in iron smelting, and as fillers for many 
purposes, etc., and it will only be possible here to outline the specification require- 
ments of a few of the more important uses. 

For many purposes in chemical industry, the limestone is first calcined to lime, 
which may be marketed as quicklime or in the hydrated form, and for this reason 
specifications frequently deal with the composition of quicklime or hydrated lime, 
rather than with that of the limestone from which they are derived. 

The particle size and rate of settling of hydrated lime from an aqueous suspension 
are important considerations for many chemical purposes, e.g. paper manufacture 
requires quick settling limes, whereas slow settling is required in treating leather. 
Surface area is important in lime used for water treatment, in making bleaching 
powder and other uses in suspension in water. 

These factors are largely determined by the characteristics of the limestone, the 
degree of burning and sometimes its subsequent treatment. The extent to which the 
lime has been exposed to air before it is slaked is important; the longer the exposure, 
the quicker will the hydrate or carbonate settle. The quantity of water used for 
slaking the lime also needs consideration; as a general rule a large excess of water 
gives a finely divided hydroxide precipitate which settles slowly, the fastest settling 
hydroxide being obtained when the quicklime is slaked with twice the theoretical 
quantity of water required. In the case of high calcium reactive quicklimes of the 
Buxton type, a large excess of water (up to 10 times the theoretical quantity required 
for hydration) may be required to produce a fine particle sized hydrate of slow 
settling characteristics. If, however, only twice the theoretical quantity of water is 



used, the product is a semi-dry hydrate which, if diluted to a milk will have fast 
settling characteristics. 

Abrasiveness is a consideration in lime used in insecticidal sprays. In wire- 
drawing hard-burned limes tend to be more abrasive than soft-burned ones and are 


A useful indication of the relative amounts of lime and limestone used by various 
industries is afforded by statistics relating to the United States which classify lime 
and limestone separately, according to the condition in which they are sold to 

Limestone (crushed and broken) sold or used by producers in the United States 
in 1958 totalled over 390 million short tons. 

The consumption (in million short tons) for the principal listed uses was as 
follows: concrete aggregate and road stone (226-7), fluxing stone (25-6), agri- 
culture (19-9), riprap (4-7), railroad ballast (4-3), miscellaneous (109). The uses 
under "miscellaneous" included: Portland cement (73-9), lime and dead-burned 
dolomite (14-5), asphalt filler (2-3), glassmaking (0-9), sugar refining (09), whiting 
(0-7), carbide manufacture (0-7) and paper-making (0-4). 

The dolomitic lime produced totalled 1-5 million long tons. It was used for 
refractory purposes, in paper manufacture and in the recovery of magnesia from 

Of the total lime produced in the United States in 1958, 67 per cent, was con- 
sumed in chemical and industrial plants, 18 per cent, (including dead burned dolo- 
mite) as a refractory material in metallurgical processes, 13 per cent, by the building 
trade and 2 per cent, for liming land. 

In chemistry and industry lime is used as a metallurgical flux, in the manu- 
facture of alkali, glass, paper and calcium carbide; in water and sewage purification; 
in soil stabilization, and in the building industry in finishing lime, mason's lime and 

Lime Burning. Although limestone is converted into lime by simple calcination, 
the economic production of good quality lime is influenced by many factors, such as 
the availability of fuel at an economic price, the size of the stone available for 
calcination and its behaviour during the process. 

As regards fuel, bituminous coal or producer gas is most commonly used in 
Great Britain. In Canada and the United States producer gas was most favoured up 
to 1957, but since that date many plants have changed over to natural gas. Fuel 
efficiency (if using other than natural gas) is most essential, as fuel can account for up 
to 50 per cent, of the total cost of producing the lime. The advantages claimed for 
gas-fired lime kilns are high conversion rates in terms of lime produced per sq. ft. of 
kiln area per twenty-four hours and the possibility of using stone down to 2-in. 
mesh size. Calcination is more readily controlled than with mixed feed kilns and the 
product is not contaminated with fuel ash. 

According to B. J. Gee, account must be taken when designing a lime kiln of the 
wide variations which may occur in the hardness, porosity, density and resistance 



to abrasion of the limestone. A highly stratified deposit tends to yield flat, elongated 
" flakey " lumps, a shape which is less desirable for use in producer gas-fired kilns 
than angular or more cubic shaped pieces. There appears to be an optimum size of 
limestone for particular kilns: thus one designed to burn stone 9 in. by 5 in. is 
unlikely to be satisfactory with 3 in. by 1 in. stone, and a very wide range of sizes 
is undesirable. A method for burning small limestone (below 3 in. size) has been 
described by Knibbs and Thyer (1957). 

The old-fashioned Hoffmann kilns require lumps varying from 40 to 60 lb., but 
modern practice in vertical kilns usually requires stone ranging from 4 in. to 6 in., 
some kilns taking as small as 2 J in. The Priest-Knibbs patent kiln can take |-li in. 
material. Rotary kilns usually require stone between J in. and 2 in. When the lime- 
stone is calcined in large lumps the outside of the lumps is often converted into lime 
before the material in the centre, and is thus subjected to much further heating 
before the whole operation is complete. The outer layer may, therefore, become 
what is termed " hard burnt " and be of a darker colour, slower in slaking and less 
reactive than correctly burnt lime. This slower rate of slaking may, however, be an 
advantage for certain purposes. 

The lime as it comes from the kiln is usually sorted into grades from " best 
hand-picked ", varying with the degree of burning to " small lime " or " lime ashes " 
which consists of the material of 1 inch and under together with cinders from the 
fuel, and clinker. Lime ashes are usually sold for agricultural use. 


Building Lime. Very considerable tonnages of limestone are used for producing 
lime for building purposes, but large quantities of such lime are used without 
having been submitted to any serious regular testing. 

B.S.I. Specification 890 : 1940 provides for two classes of both building and 
hydrated lime. Class A applies to lime for plastering, finishing coat, coarse stuff 

Table 93 

Quicklime for Building. B.S. 890 
Class A 


CaO + MgO, min. 
Insoluble matter, max. . 
Loss on ignition, max. : 

Lump .... 

Residue on slaking,* max. : 

No. 18 sieve . 

No. 52 sieve . 
Hydraulic strength at 28 days:f 



70 per cent. 
3 per cent. 

5 per cent. 
7 per cent. 

5 per cent. 
2 per cent. 

100 lb. per sq. in. 
300 lb. per sq. in. 

* By washing with water, material passing No. 1 8 sieve being 
then treated on a No. 52 sieve. 

f For semi-hydraulic quicklime only. 



and building mortars; Class B to limes for use in coarse stuff and building mortars 
only. For both classes the limes may be either of the non-hydraulic or semi-hydraulic 

The specification requirements for Class A quicklime are summarized in Table 

Tests are also specified for the volume yield of lime-putty and workablity. 

The specification requirements for Class B quicklime are the same as for Class 
A summarized above except that no minimum figure is specified for total CaO + 
MgO, nor for the residue on a No. 52 sieve (after slaking). 

A.S.T.M. Specification C 5-26 for quicklime for structural purposes recognizes 
two types, calcium lime and magnesium lime, which should comply with the require- 
ments shown in Table 94. 

Table 94 

Quicklime for Structural Purposes. A.S.T.M. C 5-26 

Calcium lime 

Magnesium lime 

Per cent. 

Per cent. 

CaO, min. 



MgO, max. . 



CaO + MgO, min. 



SiO a 4- A1 2 0» + Fe a O,, 




CO„, max. : 

If sampled at works . 



If sampled elsewhere 



In no case must the lime contain more than 15 per cent, of 
insoluble residue. 

The quicklime is also classified according to its rate of slaking under standard 
conditions of test. Limes slaking in not more than five minutes are designated as 
quick slaking, those taking from five to thirty minutes as medium, whilst slow slaking 
limes comprise those requiring over thirty minutes. The quicklime has also to 
comply with tests for workability, i.e. plasticity of the lime putty. 

Hydrated Lime. B.S.I. Specification 890 : 1940 provides for Classes A and B as 
defined above for quicklime. To comply with the specification requirements for 
Class A hydrated lime, the content of CaO + MgO must not be less than 70 per cent, 
of the sample after ignition, the remainder being principally silica and alumina. If 
the MgO exceeds 5 per cent, the material is termed magnesian lime. The insoluble 
matter must not exceed 1 per cent, or the CO2 be over 2 per cent. The fineness is 
determined by washing on two sieves successively, the maximum residue allowable 
on a 72-mesh sieve being 5 per cent., while that on 170-mesh is limited to a maximum 
of 10 per cent. 

Tests are also specified for workability and soundness, the Chatelier tests being 
used for the last named, a maximum expansion of 10 mm. being allowed. Hydraulic 
strength tests are also provided and specify the same limits as those for Class A 



The specification requirements for Class B hydrated lime are the same as for 
Class A, except no minimum is stated for the content of CaO + MgO, but the 
limit for CO2 is 5 per cent. 

Portland Cement. This industry is probably the largest consumer of limestone, 
apart from that used as a road-making or ballasting material and for the production 
of building lime. 

The manufacture of Portland cement is carried out by calcining a carefully 
proportioned mixture of calcium carbonate and silicates of aluminium; the raw 
materials being usually limestone or chalk and clay, shale or marl. The processes 
used for making Portland cement consist of (1) finely grinding the raw materials to 
give a homogeneous mixture; (2) calcining the mixture in a kiln to obtain a clinker; 
(3) finely grinding the clinker with the addition of gypsum if necessary to adjust the 
setting time. 

The general processes in use are designated respectively wet and dry, depending 
on whether the raw materials are ground and mixed in a wet or dry state. The wet 
process is the one most generally used in Great Britain, as chalk, clay marl and river 
muds are particularly adaptable to this process. In the wet process the slurry contains 
from 35 to 45 per cent, of water and the materials will mostly pass 170-mesh. In the 
wet process a large amount of fuel is required to drive off the moisture from the 
slurry, and much research has been carried out with a view to reducing the amount 
of moisture in the slurry, before it is fed into the rotary kilns. Rotary vacuum 
filters are in use at some plants in the United States, and these reduce the moisture 
content from about 42 per cent, to 22 per cent. Recently work carried out by the 
British Portland Cement Manufacturers Ltd. has shown that by using plate and 
frame presses the moisture content can be further reduced to about 18£ per cent., 
without any hold up of production. The saving of fuel thus effected is stated to be 
of the order of 25 to 40 per cent., depending on the original efficiency of the kiln. 

Dry processes have found most favour in the United States where hard raw 
materials are most generally used. 

At one time a fair number of small, stationary, vertical kilns were used for the 
calcination of Portland cement raw materials, but these have now been almost 
entirely superseded by large rotary kilns. The rotary kiln is a slightly inclined cylinder 
about 150-250 ft. in length, rotating on its axis, the finely ground raw materials 
being fed in at the upper end and travelling to the lower end where fuel is blown in 
by air blast and ignited. The calcined material leaves the kiln in the form of granules 
of clinker, mostly J to | in. size and passes to the coolers. 

The fuel used for firing rotary cement kilns in the United Kingdom is usually 
powdered coal, but waste gas from blast furnaces has been used in Scotland. In the 
United States oil, natural gas or pulverized coal are frequently used and during 
World War II electric firing was used in Switzerland using graphite electrodes and a 
low-tension arc. The power consumption amounted to about 1 1 kWh. per ton of 
clinker produced. 

Special consideration has to be given to the rotary kiln lining, which has to resist 
considerable abrasion and attack by basic materials in the mix, particularly in the 
burning zone. Ordinary firebricks are used in the cooler part of the kiln, but high 



alumina bricks containing 50 per cent, or upwards of alumina (made from bauxite 
or diaspore) or sometimes magnesia bricks, are needed for the hotter parts of the 

For a comprehensive account of the composition and properties of a large 
variety of calcareous cement products reference should be made to " The Chemistry 
of Cement and Concrete," by F. M. Lea (1956). 

Although most of the limestone used in industry is employed practically as 
quarried, in recent years there has been a tendency in the United States to use some 
beneficiation process, such as froth flotation, to render the material more suitable 
for making Portland cement. The aim of such processes is usually to reduce the 
ratios of certain constituents, such as silica, iron oxide and alumina, to that of 
calcium carbonate by removing some of the minerals in which the three oxides 
occur. The ratio of the percentage of calcium carbonate to that of alumina plus 
ferric oxide plus silica in the Portland cement mixture is of considerable practical 
importance. The removal of coarse quartz particles decreases grinding costs and the 
elimination of mica reduces the percentages of iron oxide, and alkalis, both of which 
are regarded as objectionable if present in quantity. 

Although calcium sulphate is added to the cement after calcination in order to 
regulate its setting time, the presence of sulphur in the form of sulphides, or sulphates, 
in the raw mixture before burning, is not desirable as it may lead to the formation of 
calcium sulphoaluminate, which is highly expansive. 

For use in making Portland cement which will conform to the requirements of 
British Standard Specification B.S. 12 : 1958, a limestone should not contain more 
than 2-7 per cent, of magnesia and even less if this constituent also occurs in the 
clay employed. Other impurities which may be present are often of considerable 
importance. Thus, silica sometimes occurs in the limestone in the free, or uncom- 
bined, condition as quartz, flint or chert, and in such forms may render the material 
uneconomic for cement manufacture owing to the high cost of fine grinding, but 
when present in a combined state, as in the minerals mica, hornblende or serpentine, 
it is less objectionable. Silica may also occur in a limestone in combination with 
alumina as finely disseminated clay, but in this form it is useful in cement making, 
if not present in too large a quantity. 

Although phosphate is not commonly reported in commercial analyses of lime- 
stone, if this constituent is present in amount greater than about 1 per cent. P2O5, it 
may prove objectionable as it slows down the setting time of the finished cement to 
an abnormal extent. In one case in the author's experience, the presence of 1 -5 per 
cent. P2O5 in the limestone resulted in a cement which took several days to set. 
Limestone used in the Lehigh Valley, U.S.A., for many years past contains about 
0-2 per cent. ofP 2 5 . 

Iron oxide, carbonate and silicate in small amounts form useful fluxes, but iron 
sulphides, such as pyrite, are objectionable if present in amounts much over 2 per 
cent. It may be remarked that a pure limestone is usually more difficult to grind than 
one containing a fair quantity of argillaceous impurity. 

The chemical compositions of some calcareous materials which are used in the 
United Kingdom in making Portland cement are shown in Table 95. 



Table 95 
Some British Limestones for Portland Cement Manufacture 

Medway White 

North Wales 

Blue Lias 




Per cent. 

Per cent. 

Per cent. 

Lime, CaO 




Magnesia, MgO 




Iron oxide, Fe 2 3 



Alumina, Al a O s 


Sulphuric anhydride, SO a 



1 • 

Silica, SiO, 




Carbon dioxide, CO, 




Water, H.O 

19 03 



* Not recorded. 

The proportion of limestone in a mixture for burning to ordinary Portland 
cement will vary with the composition of the clay or shale with which it is com- 
bined. As a rough guide it may be stated that a desirable mix may contain about 75 
per cent. CaC0 3 ; 20 per cent. Si02 + AI2O3 + Fe203, the remaining 5 per cent, 
being impurities such as MgO and alkalis. The percentage of Si02 in the mixture 
should about equal that of Fe2C>3 + AI2O3. 

British Standard Specification B.S. 12 : 1958 for Portland Cement (ordinary and 
rapid hardening) provides tests for fineness, chemical composition, strength, setting 
time and soundness. The fineness of the cement is determined from a consideration 
of its specific surface value, which, when determined by a prescribed method, shall 
be not less than 2,250 sq. cm./gm. for ordinary Portland cement and 3,250 sq. 
cm./gm. for rapid hardening Portland cement. 

As regards chemical composition, the cement has to comply with the following 

(1) Lime saturation factor: The lime saturation factor (L.S.F.) shall not be 
greater than 102 or less than 0-66 when calculated by the formula 


(CaO) + 0-7(SO 3 ) 

2-8(Si0 2 ) + 1-2(A1 2 3 ) + 65(Fe 2 O 3 ) 

where each symbol in brackets refers to the percentage (by weight of total cement 
of the oxide, excluding any contained in the insoluble residue referred to below. 

(2) Insoluble residue: The weight of insoluble residue, as determined by the 
prescribed method shall not exceed 1 -5 per cent. 

(3) Magnesia: The weight of magnesia contained in the cement shall not exceed 
4 per cent. 

(4) Alumina-iron ratio : The ratio of the percentage of alumina to the percentage 
of iron oxide shall be not less than 0-66. 

(5) Sulphuric anhydride: The permitted content of total sulphur in the cement, 
expressed as SO3, shall not exceed the appropriate figure in the following table: 



Tricalcium aluminate Maximum total sulphur 

expressed as SOa 
(Percentage by weight) 

7 or less 2>5 

Greater than 7 3-0 

The tricalcium aluminate content (C3A) is calculated by the formula 
CsA = 2-65(Al 2 3 ) — l-69(Fe 2 3 ), 

where the symbols have the same meaning as in (1) above. 

(6) Loss on ignition: The total loss on ignition shall not exceed 3 per cent, for 
cement in temperate climates or 4 per cent, for cement in tropical climates. 

The setting time of the cement, when tested by the prescribed method, shall be as 
follows: initial setting time not less than forty-five minutes, final setting time not 
more than ten hours. 

Table 96 

Portland Cement. A.S.T.M. C 150-56 











Per cent. 

Per cent. 

Per cent. 

Per cent. 

Per cent. 

Silica, SiOz, min. .... 






Alumina, AI2O3, max. 






Ferric oxide, Fea03, max. . 






Magnesia, MgO, max. 






Sulphur trioxide, SO3 : 

when 3CaO.Al203 is 8 per cent, or 

less, max. ..... 






when 3CaO. AI2O3 is more than 8 per 

cent., max. ..... 


. — 




Loss on ignition, max. 






Insoluble residue, max. 






Tricalcium silicate, 3CaO.Si02,t max. 






Dicalcium silicate, 2CaO . SiOz.t min. . 






Tricalcium aluminate, 3CaO.Al203,t 






* The calcium aluminate shall not exceed 5 per cent, and the tetracalcium alumino- 
ferrite (4CaO.Al203.Fe203> plus twice the amount of tricalcium aluminate shall not 
exceed 20 per cent. 

t The expressing of chemical limitations by means of calculated assumed compounds 
does not necessarily mean that the oxides are actually or entirely present as such compounds. 
The percentages of tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetra- 
calcium aluminoferrite shall be calculated from the chemical analysis as follows: 

Tricalcium silicate = (4-07 x % CaO) - (7-60 x % SiO a ) - (6-72 x % A1 2 8 ) - 
(1-43 x % Fe 2 3 ) - (2-85 x % SO3). 

Dicalcium silicate = (2-87 x % SiO a ) - (0-754 x % 3CaO.SiOa) 

Tricalcium aluminate = (2-65 X % AI2O3) - (1-69 x % Fe 2 3 ) 

Tetracalcium aluminoferrite = 3-04 X % Fe20s. 

Oxide determinations calculated to the nearest 01 per cent, shall be used in the calcula- 
tions. Compound percentages shall be calculated to the nearest 01 per cent and reported 
to the nearest 1 per cent. 



Tests are also specified for setting time, tensile and crashing strength and sound- 

A.S.T.M. Specification C 150-56 provides for five types of Portland cement: 
type I, for general concrete construction where the special properties of other types 
are not required ; type II, for general use in concrete which will be exposed to moder- 
ate sulphate action or where moderate heat of hydration is required; type III, where 
high early strength is required; type IV, where low heat of hydration is desirable; 
type V, where high sulphate resistance is required. The physical tests include fineness, 
soundness, setting time, and tensile and compressive strengths of cement-sand 

The chemical requirements of the five types are shown in Table 96 (see p. 301). 

The cement has also to comply with a number of physical requirements, in- 
cluding those for fineness, soundness, setting time of the neat cement and compres- 
sive strength and tensile strength of cement-mortar test pieces and the air content 
of a mortar prepared according to A.S.T.M. C 185. 

British Standard Specification B.S. 146 : 1958 for Portland blast-furnace cement 
requires the material to consist of a mixture of Portland cement clinker and 
granulated blast-furnace slag. The two materials may be mixed together in such 
proportions as the manufacturer may prefer, subject to the proviso that in no case 
shall the proportion of slag exceed 65 per cent, by weight of the total quantity. 
The granulated blast-furnace slag shall be added to the Portland cement clinker and 
the whole ground together so that the two constituents shall be thoroughly and 
intimately mixed and shall produce a cement capable of complying with this British 
Standard. No materials, other than gypsum (or its derivatives) or water or both, 
shall be added during the grinding of the Portland cement clinker and granulated 
blast-furnace slag. 

The specification provides tests for fineness, chemical composition, strength, 
setting time and soundness. The fineness of the cement is determined from consider- 
ation of its specific surface value, which, when determined by the prescribed method, 
shall not be less than 2,250 sq. cm./gm. As regards chemical composition, the 
Portland cement clinker portion of the mixture shall comply, where applicable, with 
the requirements of B.S. 12 " Portland Cement," and the cement as a whole shall 
comply with the following conditions : Insoluble residue not to exceed 1 -5 per cent. ; 
magnesia not to exceed 7 per cent. The sulphuric anhydride content of the cement 
shall not exceed 3 per cent, and the sulphur present as sulphide shall not exceed 
1-5 per cent.; those percentages being equivalent to a maximum total of 6-75 per 
cent, sulphuric anhydride. The total loss on ignition shall not exceed 3 per cent, for 
cement in temperate climates and 4 per cent, for cement in hot climates. Com- 
pressive strength tests for mortar cubes at three, seven and twenty-eight days after 
gauging are provided. 

Portland blast-furnace slag cement is specified in A.S.T.M. C 205-58 T, which 
provides for two types of hydraulic cement, ordinary and air-entraining. It requires 
the product to be an intimately interground mixture of Portland cement clinker and 
granulated blast-furnace slag, the slag constituting not less than 25 per cent, or 
more than 65 per cent, of the mixture. The Portland cement clinker constituent shall 



conform to the chemical requirements laid down for type I cement in A.S.T.M. 
C 150-56. The chemical composition of the Portland blast-furnace slag cement shall 
be that shown in Table 97. 

Table 97 

Portland Blast-furnace Slag Cement. A.S.T.M. C. 205-587 

Magnesia, MgO, max. 
Sulphur trioxide, SO3, max 
Manganic oxide, MmO.}, max. 
Sulphide sulphur, S, max. 
Insoluble residue, max. . 
Loss on ignition 

At the option of the manufacturer materials may be used as grinding aids, 
provided that they have been shown to be not harmful, in the amounts indicated, by 
tests carried out or reviewed by the appropriate committee. The committee has 
declared as not harmful inclusion of the following materials in the manufacture of 
Portland cement under A.S.T.M. Specification C 150-56: the material known com- 
mercially as TDA (composed of triethanolamine and highly purified soluble calcium 
salts of modified lignin sulphonic acids) manufactured by the Dewey and Almy 
Chemical Company, when added in an amount not exceeding 043 per cent, by 
weight of the cement, except that in type III a maximum of 08 per cent, by weight 
may be used; the material known commercially as " 109-B " (composed essentially 
of 2 methyl 2-4-pentane diol) marketed by the Master Builders' Company, when 
added in an amount not exceeding 03 per cent, by weight of the cement, except 
that in type III cement a maximum of 05 per cent, by weight may be used. 

The cement has also to comply with a number of physical requirements, includ- 
ing those for fineness, soundness, setting time of the neat cement, compressive 
strength and tensile strength of cement-mortar test pieces and the air-content of a 
mortar prepared according to A.S.T.M. C 185. 

The granulated blast-furnace slag constituent shall conform to the following 
composition : 

CaO + MgO + I/3AI2O3 

Si0 2 + 2/3 AI2O3 

> 1 

Granulated blast-furnace slag having a chemical composition within the limits 
shown below generally meets the requirements of the above formula. 

Per cent. 

Silicon dioxide, SiO a . . 30-40 

Aluminium oxide, AI2O3 8-18 

Ferrous oxide, FeO .0-1 

Calcium oxide, CaO . . 40-50 

Magnesium oxide, MgO . 0- 8 

Manganic oxide, Mn203 0- 2 

Sulphide sulphur, S . .0-2 



Both types of Portland blast-furnace slag cement have also to satisfy specification 
requirements in regard to fineness, soundness, setting time, compressive strength 
and tensile strength of cement-sand briquettes. 

An A.S.T.M. Specification C 358-58 covers slag cement for use as a blend with 
Portland cement in making concrete and as a blend with hydrated lime for making 
masonry mortar. 

Portland-pozzalan cement is dealt with in A.S.T.M. Tentative Specification 
C 340-55T which covers two types, ordinary and air-entraining cements. The 
cement is required to be an intimately interground mixture of Portland cement 
clinker and pozzalan, or an intimate and uniform blend of Portland cement and 
fine pozzalan. The pozzalan constituent shall be not less than 15 per cent, by weight 
or more than 50 per cent, by weight of the Portland-pozzalan cement. The pozzalan 
shall be a siliceous or siliceous and aluminous material, which in itself possesses 
little or no cementitious value but will in a finely divided form and in the presence of 
moisture chemically react with calcium hydroxide at ordinary temperatures to form 
compounds possessing cementitious properties. Pozzalans which may be employed 
include such natural materials as certain diatomaceous earths, opaline cherts and 
shales, tuffs, and volcanic ashes or pumicites and some of the more common clays 
and shales of the montmorillonite and kaolinite types, and such artificial materials 
as precipitated silica and some of the fly ashes. Water or untreated calcium sulphate, 
or both, may be added in amounts such that the limits provided for ignition loss and 
sulphur trioxide are not exceeded. The chemical requirements specify the following 
maximum percentage limits: Magnesium oxide (MgO), 5 0; sulphur trioxide (SO3X 
2-5; loss on ignition, 3 0. Specification requirements are also provided for physical 

Waterproofed Portland cement is ordinary Portland cement to which has been 
added during grinding a small proportion of calcium stearate or a non-saponifiable 
oil. One proprietary brand of waterproofed cement contains a product obtained by 
treating gypsum with tannic acid. 

Air-entraining additions include a wide variety of products, such as synthetic 
detergents of the alkyl-aryl sulphonate type, calcium salts of glues and other pro- 
teins, calcium lignosulphonate derived from the sulphate process of papermaking, 
sodium salts of cyclo-paraifin carboxylic acids obtained in petroleum refining. 

At one time constructional engineers endeavoured to make concrete containing 
as few air bubbles as possible, but with recent developments the addition of air- 
entraining agents has become common practice for many purposes. The agent, 
when the concrete is mixed, produces a foaming and forms bubbles in the concrete. 
Such air-entrained concrete absorbs the expansion caused by freezing, without 
flaking or cracking, and so is particularly valuable for highway construction. 
Roads made with air-entrained concrete were first laid down about twenty years ago 
and since that time many thousands of miles of such roads have been constructed in 
the United States, and thirty-eight States now specify air-entrained cement for then- 
cons truction. 

A.S.T.M. Specification No. C 175-56 for air-entraining Portland cement pro- 
vides for three grades, the chemical composition of which corresponds to those of 



types I, II and HI for Portland cement as specified in A.S.T.M. C 150-56. It differs, 
however, in regard to certain of the requirements for physical properties. 

Prepared masonry cements, produced by intergrinding Portland cement clinker, 
or finished Portland cement, with limestone and an air-entraining plasticizer are 
rinding increasing use in the United States. The product has the high plasticity and 
water-retaining properties which are essential in mortars for brick and other 
masonry work. These prepared masonry cements are made by over 100 Portland 
cement plants in the United States to the extent of about 12 million barrels per 

B.S.S. 1370 : 1958 covers a type of Portland cement intended for use in structures 
where large masses of concrete have to be placed. The types of concrete work for 
which the cement is especially suited include concrete dams and many other types of 
water-retaining structures, bridge abutments, massive retaining walls, piers and 
slabs, etc. In large masses of concrete there is often a considerable rise in temperature 
resulting from the heat evolved as the cement sets and hardens and from the slow 
rate at which it is dissipated from the surface. The shrinkage which occurs on sub- 
sequent cooling sets up tensile stresses in the concrete which may result in cracking. 
The use of a cement of the type covered by this specification is advantageous since it 
evolves less heat than ordinary or rapid hardening Portland cement. The rate of 
strength development of low heat Portland cement is lower than that of ordinary 
Portland cement, but the ultimate strength is not reduced. 

The heat evolved by a cement as it reacts with water and sets and hardens is 
termed the heat of hydration. A test for the total amount of heat evolved after 
seven and twenty-eight days is included in the specification. 

As regards chemical composition, the cement must satisfy the following require- 
ments : the percentage of lime, after deduction of that necessary to combine with the 
sulphuric anhydride present shall not be more than 2-4 times the percentage of 
silica, plus 1-2 times the percentage of alumina, plus 0-65 times the percentage of 
iron oxide, and shall be not less than 1 -9 times the percentage of silica, plus 1 -2 times 
the percentage of alumina, plus 0-65 times the percentage of iron oxide. The ratio 
of the percentage of alumina to the percentage of iron oxide shall be not less than 
0-66. The weight of insoluble residue as determined by the specified method shall 
not exceed 1 -5 per cent., that of magnesia shall not exceed 4 per cent, and the total 
sulphur content, calculated as sulphuric anhydride (SO3) shall not exceed 2-75 per 
cent. The total loss on ignition shall not exceed 3 per cent, for cement in temperate 
climates and 4 per cent, in tropical climates. 

The cement when tested for fineness by the prescribed method shall have a specific 
surface of not less than 3,200 sq. cm./gm. 

The heat of hydration of the cement when tested by the prescribed method shall 
be not more than 60 calories per gm. at seven days and not more than 70 calories 
per gm. at twenty-eight days. 

Tests are also specified for compressive strength, setting time and soundness. 

Natural Cements. As the name indicates, these products are made by calcining 
a clayey limestone in its natural state without the addition of clay or shale. At one 
time these cements were produced in considerable quantities on the Continent and 



in the United States, but for many years past the output has declined in the face of 
competition from Portland cement of standard composition. Natural cement is 
usually produced by calcining the raw limestone in lumps, any underburned material 
being rejected before grinding. Natural cement from different localities varies 
considerably in composition, some containing from 15 to 18 per cent. MgO; about 
2-5 per cent. AI2O3, and from 18 to 25 per cent. Si02. 

A Specification for natural cement A.S.T.M. C 10-54 covers two types of material : 
type N— natural cement for use (with Portland cement) in general concrete con- 
struction, and type NA— air-entraining natural cement for the same uses as type N. 
For the purpose of the specification natural cement is defined as the product ob- 
tained by finely pulverizing calcined argillaceous limestone. The temperature of 
calcination shall be no higher than that necessary to drive off carbonic acid gas. No 
addition to this product shall be made subsequent to calcination, other than water 
and/or untreated calcium sulphate, except that for air-entraining natural cement an 
addition shall be interground that will produce air-entraining natural cement 
meeting the requirements of this specification. Furthermore, when desired by the 
consumer a quantity of calcium chloride not exceeding 2 per cent, shall be added to 
the air-entraining natural cement during manufacture in order to compensate for 
loss of strength due to air-entrainment. As regards chemical requirements the in- 
soluble residue shall not be less than 2 per cent, and the loss on ignition must not 
exceed 12 per cent. Tests also have to be satisfied regarding fineness (specific surface 
area), soundness (autoclave expansion test), time of setting and compressive strength 
of cement/sand cubes. The air-entraining type has to satisfy a test for the air content 
of a mortar consisting of 25 per cent, natural cement and 75 per cent, non-air- 
entraining Portland cement. 

Hydraulic Limes. Limestones containing about 18 per cent, of clayey matter are 
often termed hydraulic limestones, whilst those with over 20 per cent, are classified 
as eminently hydraulic limestones. 

Such material, when suitably burnt, slakes but slowly and gives a product which, 
after fine grinding and mixing with water, will set to a hard cement-like body. Hence 
hydraulic limes provide a useful building material where a product of less strength 
than Portland cement, but more easily manufactured, can be used. Considerable 
quantities of hydraulic cement have been made and used in many countries, par- 
ticularly in the United States, Belgium and France. A product known as Scott's 
cement is made by mixing feebly hydraulic lime with plaster of Paris in suitable 

Hydraulic hydrated lime for structural purposes is dealt with in A.S.T.M. 
Specification C 141-55. Hydraulic hydrated lime may be used for scratch or brown 
coat of plaster, for stucco, for mortar, and as sole cementitious material in concrete, 
or in Portland cement concrete, either as blend, amendment or admixture. Accord- 
ing to the specification hydraulic hydrated lime is the hydrated dry cementitious 
product obtained by calcining a limestone containing silica and alumina to a 
temperature short of incipient fusion so as to form sufficient free lime to permit 
hydration and at the same time leave unhydrated sufficient calcium silicates to give 
the dry powder, meeting the prescribed requirements, its hydraulic properties. The 



hydraulicity may be increased by the addition of pulverized Portland cement 
clinker, or a pulverized pozzalan, either natural or artificial. 

The products are divided into two main groups : high calcium hydraulic hydrated 
lime, containing not more than 5 per cent, of magnesium oxide, and magnesium 
hydraulic hydrated lime, containing more than 5 per cent, magnesium oxide. 

Hydraulic hydrated limes vary both in chemical composition and hydraulic 
properties and for the purpose of this specification they are divided into two types 
conforming as regards chemical composition to the requirements shown in Table 98, 
the composition being calculated on the non-volatile material. 

Table 98 

Hydraulic Hydrated Limes for Structural Purposes. A.S.T.M. C 141-55 

Type A 






Calcium and magnesium oxides (CaO and MgO) 

Silica (Si0 2 ) 

Iron and aluminium oxides (Fe2C>3 and AI2O3) 
Carbon dioxide (CO2) 

Per cent. 


Per cent. 

Per cent. 

Per cent. 

For both types the residue on a No. 30 (590 micron) sieve shall not exceed 0-5 per 
cent, and the residue on a No. 200 (74 micron) sieve shall not exceed 10 per cent. 
The neat lime paste mixed to normal consistency shall not develop an initial set in 
less than two hours as determined by the Gillmore needle method and the final set 
shall be attained within forty-eight hours. Tests are also provided for soundness and 
compressive strength. 

Pozzolana Cements. Slaked lime is an essential component of various types of 
pozzolana hydraulic cements, which are made by mixing a slurry of slaked lime with 
natural pozzolana (a siliceous volcanic material), trass, santorin earth, lightly 
calcined clay or finely ground blast-furnace slag. As magnesia has little or no reactive 
value towards these materials, it is desirable to use a high calcium lime. Pozzolana 
cements are more extensively used for building purposes abroad than in Great 
Britain. Natural pozzolanas are materials which usually owe their activity to one or 
more of the following : (1) volcanic glass ; (2) opal ; (3) clay minerals ; (4) zeolites ; (5) 
hydrated oxides of aluminium. Artificial pozzolanas include fly ash from flue stacks 
from plant using pulverized coal as fuel; ground brick, tile or pottery; burned oil- 
shale, etc., which owe their activity to glasses produced by fusion or reconstitution 
of the original components. 

In recent years considerable use has been made of fly ash mixed with lime as a 
pozzolan material. Fly ash is the finely divided residue which results from the 
combustion of ground or powdered coal and is transported from the boiler by flue 
gases. A specification for such pozzolanic material is given in A.S.T.M. C 379-56T, 
which defines the pozzolan as a siliceous or alumino-siliceous material which in 



itself possesses little or no cementicious value, but which in finely divided form and 
in the presence of moisture will chemically react with alkali and alkaline earth 
hydroxides at ordinary temperatures to form, or assist in forming, compounds 
possessing cementicious properties. The fly ash for such use is required to conform to 
the following: moisture content, max., 10 per cent. ; water soluble fraction, max., 10 
per cent. ; fineness, wet sieved amount retained on No. 30 sieve, max., 2 per cent. ; 
on a 200 sieve, max., 30 per cent. Limits are also stipulated for the minimum 
compressive strength of lime-fly ash cubes at seven and twenty-one days after 


Metallurgical Uses. Both limestone and lime are used in very considerable 
quantities as fluxing materials in blast-furnaces, open hearth furnaces and electric 
steel plants. 

Non-ferrous metallurgy also consumes an important but much smaller quantity. 
Stone for these purposes is usually required to be delivered in sizes ranging from £ 
to 6 in. in diameter. It should be strong and sound, and able to withstand heating 
without breaking up ; some limestone-marbles on heating decrepitate into powder. 

The chemical composition of the stone required differs according to the use to 
which it is to be put, the class of iron or steel to be made and the process used. In 
ferrous metallurgy the limestone serves as a flux for the removal of silica and alumina, 
and hence the content of these constituents should be low. The percentage of phos- 
phorus must be small, say not more than 001 per cent., when making low phos- 
phorus iron, but for basic iron smelting a fairly large content of phosphorus is 
desirable, sometimes as high as 1 -5 per cent. 

For use in the blast-furnace, limestone should not, as a rule, contain more than 
1 -5 per cent. Si02, although occasionally material containing as much as 5 per cent, 
is used. Sulphur should not exceed 0-5 per cent., but the quantity in limestones 
rarely exceeds this limit unless the stone is mineralized with pyrites. 

The effect of magnesia in fluxing stone is a somewhat debatable point but most 
of the limestone used for this purpose in the United States contains up to 10 per 
cent, of MgCOs and dolomite has been used successfully in Great Britain. 

For some years past, high-magnesia limestone has been used successfully at 
several large works in the United States, particularly at Bethlehem, Pa., and 
Birmingham, Ala. 

Basic open-hearth steel makers require a stone having a high lime (CaO) content 
with low sulphur and phosphorus. Silica is more objectionable in limestone for this 
purpose than in limestone used as a flux in blast-furnace work and should therefore 
be low, preferably not over 1 per cent. 

The upper limit for MgO is often put at 5 per cent., as magnesia is only a poor 
remover of phosphorus. 

When considering the suitability of a limestone for use as a metallurgical flux it 
should be borne in mind that it is the available lime which is of value, i.e. the amount 
remaining after deducting from the total the quantity required to flux the impurities 



in the limestone. Roughly, it may be assumed that 1 lb. of CaO or 1 -8 lb. of lime- 
stone is required to flux each 1 lb. of silica or alumina present. 

Metallic Calcium and Its Alloys. During the past twenty years, metallic calcium 
has slowly gained importance in metallurgical practice. Before World War II, the 
small demand for the metal was met chiefly by the productions of Germany and 
France, but in 1 939, in view of the possible curtailment of supply by war, a plant was 
put into operation at Sault Ste. Marie, Michigan, U.S.A., by the Electro Metallurgi- 
cal Company. 

Canada is now the largest producer of metallic calcium and produced 66,341 lb. 
in 1957. 

The metal is usually produced: (1) by the electrolysis of fused calcium 
chloride, in which the calcium is deposited on a vertical upward-moving cathode; 
the metal so obtained is cast into slabs which have a purity of about 95-98 per 
cent, and are free from calcium chloride; (2) by a modification of the Pidgeon 
process using ferrosilicon as the reducing agent and operating in a vacuum. 

In the Pidgeon-MacCarthy thermic process lime of at least 97 per cent, purity 
and carrying not over 1 per cent. MgO is briquetted with 5 to 20 per cent, excess of 
aluminium powder. The briquettes are heated in a vacuum of 10 mm. to about 
1,170°C. in a retort. The calcium vapour evolved is condensed in a zone kept at 
740-680° C. and any metallic magnesium vapour is condensed in another zone 
maintained at 350-275° C. The reactions occurring during the process are as follows: 
5CaO + 2A1 = 3Ca + (CaO)aAl 2 C>3 

3MgO + 2CaO + 2A1 = 3Mg + (CaO^AkOs 

Some of the physical properties of pure metallic 

Atomic number 

Atomic weight 

Atomic volume 

Isotopes (6) 

Crystal structure 

at room temperature 

at elevated temperatures . 

above 450°C. 
Melting point . 
Boiling point 

Density at room temperature 
Specific heat (0-100°C.) 
Latent heat of fusion . 
Thermal conductivity (at 20°C.) 
Electrical conductivity (relative to silver at 20° C.) 
Young's modulus 

calcium are as follows: 


40 08 


40, 42, 43, 44, 46, 48. (40 

most abundant, 96-76 per 


face-centred cubic, a = 5-56A 
body-centred cubic 
hexagonal close packed 
851° C. 
0056 lb./in. 3 
0149 cal./gm./°C. 
78-5 cal./gm. 
0-3 cal./cm.2/cm./°C./sec. 
45 per cent. 
3 x 10«p.s.i. 

16 Brinell (approx.) : Rockwell 
" B " 36-40. 



Four grades of metallic calcium are produced by Dominion Magnesium Ltd. of 
Haley, Ontario, Canada: (1) chemical standards grade, with a purity of 99-8 per 
cent, and supplied in granules (—4 to + 30-mesh); (2) special purity grade contain- 
ing 99-9 per cent. Ca + Mg (Mg. max. 0-5 per cent.), available in granules, lump or 
extruded forms; (3) high purity calcium containing 99-99-5 per cent. Ca, with the 
following maxima for impurities, Mg 0-75, N 015, Al 0-30, available in granules, 
lumps, extruded forms or billets; (4) commercial calcium with 98-99 per cent. Ca, 
and 0-5-1 -5 per cent. Mg, N 1 per cent. max. Al 0-35 per cent, max., available in 
granules, crystalline lumps, extruded forms, billets and ingots. 

Metallic calcium requires for its production a high grade lime containing the 
smallest possible percentages of magnesium, barium, strontium and alkalis. One 
lime used showed the following percentage analysis: CaO, 97-55; MgO, 0-65; Si02, 
0-7; Fe203 + AI2O3, 0-6; Na20 + K2O, 00009, with barium and strontium absent. 
The presence of the alkali metals is particularly undesirable, as they may cause the 
ignition of the metallic calcium when the retort is opened. 

The principal use for metallic calcium is as a reducing agent in the production 
of metals such as uranium, thorium, titanium, zirconium or chromium from their 
oxides or fluorides. The metal finds use in metallurgy as a deoxidizer and scavenger 
in the refining of certain non-ferrous metals and alloys, such as those of copper, 
aluminium, chromium and nickel. It is used to remove bismuth from lead and the 
presence of about 04 per cent, of calcium is claimed to increase the tensile strength 
of lead for use in cable sheaths. It is also a minor constituent of certain other alloys. 

The metal reacts readily with nitrogen at about 90° C. but not with argon and so 
can be employed to remove the last traces of nitrogen from this gas. 

Alloys of calcium with barium, aluminium or magnesium have been used as 
" getters " in vacuum tube manufacture. Calcium is commonly used in magnesium 
foundries, up to -25 per cent, being added to give an improved surface on magnesium 
base castings. 

Lead alloys containing calcium are becoming increasingly important particularly 
for storage battery use where 01 per cent, calcium produces an alloy equivalent 
and in some respects superior to 9 per cent, antimony. 

In the manufacture of some types of steel, metallic calcium, or its alloys, such as 
calcium-silicon or calcium-manganese-silicon are used as deoxidizers and scavengers 
to give uniformity in the castings and to improve machinability, the calcium- 
manganese-silicon alloy used for the purpose contains 16-20 per cent, of calcium, 
14-18 per cent, of manganese and 53-60 per cent, of silicon. 

Calcium boride has found some commercial applications as a deoxidizer for 
copper and other non-ferrous alloys, as a reducing agent, and as a source of boron 
for the preparation of metallic borides. It can be produced by the electrolysis of a 
fused mixture of boric oxide, lime and calcium chloride. 

Calcium Hydride, which has the formula CaH2, has been available commer- 
cially, in varying degrees of purity, since about 1912. 

During World War II large quantities of calcium hydride were made by Metal 
Hydrides Inc. of Beverly, Mass., for use by the military forces as a source of 



Calcium hydride, as produced by Metal Hydrides Inc., of Beverly, Mass., 
U.S.A., is in the form of greyish-white prismatic crystals of 93-96 per cent, purity. 
It serves as a convenient source of pure (but wet) hydrogen, 1 gm. gives 1 1. at n.t.p. 
At high temperatures it is a very powerful, but controllable, reducing agent: re- 
fractory oxides such as TiC>2 can be reduced to the metal at temperatures below 
their melting points. It is a useful drying agent for some organic solvents and for 
gases, such as hydrogen, argon, helium, etc. In organic chemistry it is useful as a 
condensing agent and as a co-catalyst. 

Alkali Manufacture. Large quantities of high calcium limestone are used in the 
manufacture of soda ash by the ammonia-soda process, as each ton of soda ash 
made requires about 1-1 -25 tons of limestone. Preference is usually shown for stone 
in lumps between 1 and 4 in. in diameter. 

As a general rule, arenaceous or argillaceous limestones are unsuitable owing to 
their content of silica, and dolomite is also considered to be uneconomical, but 
limestone containing up to 6 per cent. MgO is tolerated by some alkali manufacturers. 
A specification proposed by one United States authority suggests the following 
percentage composition as desirable : CaCOs, 90-99 ; MgCC>3, • 6 ; Fe203 + AI2O3 + 
Si02, 0-3. For use in the Leblanc soda process the stone should be of pea size and 
contain about 96 per cent. CaCC>3 with only small amounts of alumina, silica and 
magnesia. Silica and alumina are objectionable as they may cause the formation of 
silicates of aluminium and sodium; bituminous matter is not deleterious. 

In the manufacture of caustic soda from soda ash, lime is used either in the form 
of quicklime, hydrated lime or milk of lime. The lime should be fairly pure and free 
from clayey matter or core, and although magnesian lime is not suitable, a small 
percentage of magnesia, possibly up to 3 per cent., is permissible: in the United 
States a material containing 85 per cent, of available lime is considered to be a fair 
standard, but 70 per cent, is regarded as being too low to be economical. It should 
not contain impurities which will cause too rapid settling of the precipitated calcium 
carbonate from the solution, a matter which can only be determined by practical 
trial in the plant. 

Sugar Refining. Lime is used in the manufacture of both cane and beet sugar, 
either to precipitate impurities from the juices or syrups or, as in the Steffen process, 
to precipitate sugar from impure solutions. Silica is objectionable in limestone for 
making lime for use in sugar manufacture as it may become colloidal in the juices, 
form films on the crystals, and retard their growth. Iron oxide should be low as it 
tends to colour the finished sugar. Both quicklime and hydrated lime are employed. 
As sugar manufacturers usually require CO2 as well as lime they generally prefer to 
purchase limestone rather than lime. 

The specifications recommended by the United States Bureau of Standards in 
Circular No. 207 of 1925, entitled " Recommended Specifications for Limestone, 
Lime Powder and Hydrated Lime for Use in the Manufacture of Sugar," are 
summarized in Table 99. 

The lime powder and hydrated lime must be of such fineness that 98 per cent, 
will pass a No. 200 sieve, but the material must not be so fine that it will " ball" 
when rotated on a 40-mesh bolter at 20° C. 



Table 99 

Limestone and Lime for Sugar Refining. U.S. Bur. Standards 

lime, (min.) 



Loss on ignition, 

Limestone for the Steffen process* 
Limestone for other processes* . 
Quicklime for the Steffen process 
Quicklime for other processes . 
Lime powder ..... 
Hydrated lime 

Per cent. 

Per cent. 

Per cent. 



* The limestone is calcined before analysis. 

Paper Manufacture. Limestone and lime are extensively used in paper manu- 
facture, both in the liquor used for cooking rags, and for preparing the solutions 
used in the sulphite and sulphate processes for producing paper pulp from coniferous 
woods. Lime is also used in the recovery of caustic soda from waste liquors. 

Quicklime and hydrated lime for cooking rags in paper manufacture are covered 
by A.S.T.M. Specification C 45-25 which requires the material to be clean and free 
from gritty substances. The available lime should be 90 per cent, in quicklime and 
64-3 per cent, in hydrated lime. 

The standards suggested are put forward as those desirable, but non-compliance 
need not involve rejection of the material, as it is realized that higher or lower 
percentages may be acceptable to users under suitable conditions. 

For the soda and sulphate pulp processes of paper manufacture a high calcium 
lime with less than 2 per cent. MgO is usually preferred, and, although limes con- 
taining up to 7 per cent, total Fe203 + AI2O3 + Si02 are used, purer lime is to be 
preferred. If, however, the milk of lime process for sulphite pulp manufacture is 
used, a high magnesian lime is often preferred, particularly for treating coniferous 
woods, owing to the fact that magnesium bisulphite has greater stability, solubility 
and reactivity than calcium bisulphite. 

When the acid-bisulphite liquor is made by the Jennser tower process, in which 
sulphur dioxide gas is passed up a tower packed with limestone, a high magnesian 
limestone is undesirable, as it breaks down and clogs the tower, thus hindering the 
gas absorption. 

According to A.S.T.M. Specification C 46-27 quicklime for use in sulphite 

Table 100 

Quicklime for Use in Sulphite Pulp Manufacture. A.S.T.M. C 46-27 

Calcium lime 

Magnesian lime 

Lime, CaO, min. 
Magnesia, MgO 
Iron oxide, Fe 2 O s ; alumina, 
silica, Si0 2 , max. 

Al,O s ; and 

Per cent. 
2-5, max. 


Per cent. 
39-6, min. 




paper pulp manufacture may be either calcium or magnesian lime. Samples taken at 
the place of manufacture should have the chemical compositions shown in Table 100. 

Glass Manufacture. This usually calls for a material ground to between 20 and 
100-mesh. High calcium limestone is used for making bottle and window glass, but 
dolomitic stone is used for certain special glasses. For the production of the better 
grades of glass, limestone should contain only a small percentage of iron oxide, 
usually not exceeding 0-2 per cent., but for flint glass the limit is about 03 per 
cent. Organic matter should not exceed 0-3 per cent. 

British Standard Specification B.S. 3108 : 1959 for limestone for making colour- 
less glasses replaces that issued by the Society of Glass Technology in 1937 and 
revised in 1943 and 1956. The present specification was drawn up in close co- 
operation with the Society and was published under the authority of the Glass 
Industry Standards Committee. The Society of Glass Technology Specification 
included general recommendations for the inspection of the sample of limestone for 
obvious impurities, such as magnetic materials or unusual mineral formations. No 
limits were specified for these items and they were, therefore, not included as a 
mandatory part of the present standard, but as an appendix. For the purpose of the 
British Standard Specification a colourless glass is one which has no appreciable tint 
when viewed through the thickness normally encountered in practice. As regards 
fineness, limestone for use in tank furnaces should leave no residue on a -fc in. 
sieve and not more than 25 per cent, should pass a No. 120 B.S. sieve. Limestone 
intended for use in pot furnaces should leave no residue on a J in. sieve and not more 
than 5 per cent, should remain on a No. 14 B.S. sieve. The chemical composition of 
the limestone must satisfy the following requirements : the calcium content, expressed 
as calcium oxide (CaO), shall be not less than 55-2 per cent, (expressed as calcium 
carbonate, 98-5 per cent.); the total iron content, expressed as ferric oxide (FeaOa) 
shall not exceed 035 per cent.; total non-volatile matter (including silica) in- 
soluble in hydrochloric acid, shall not exceed 1 per cent., and organic matter is 
limited to 01 per cent. Colouring elements, other than iron, shall not be present to 
an extent sufficient to produce a detectable colour in the glass and if impurities, 
such as manganese, lead, sulphur and phosphorus, are present to the extent of 01 
per cent, individually (when expressed as oxide) their presence and amount shall be 
declared by the vendor. Any limiting value for alumina (AI2O3) and magnesia 
(MgO) shall be the subject of agreement between buyer and vendor. The maximum 
acceptable percentage moisture content of the limestone as received shall be agreed 
between buyer and vendor, but shall normally not be greater than 2 per cent. 

A recommended specification for limestone, lime and hydrated lime, for use in 
the manufacture of glass, was issued in 1921 by the United States Bureau of 
Standards in Circular 118. According to this specification any lime containing a total 
of more than 83 per cent, of lime and magnesia may be regarded as suitable, pro- 
viding the amounts of certain impurities are within specified limits. The day-to-day 
deliveries of material should not vary in their lime content by more than 2 per cent. 
The specification recognizes three classes of product as shown in Table 101 . 

A high magnesia limestone is sometimes preferred at some plants in the United 
States which use automatic processes. 



Table 101 

Limestone and Lime for Glass Making. U.S. Bureau of Standards 

Lime and magnesia, CaO + MgO 

Iron oxide, Fe 2 3 

Alumina, A1 2 3 

Sulphur + phosphorus, SO s + P a 5 

Silica, SiOj .... 

Class ! 
Max. Min. 

Per cent. 
— 94 
0-2 — 
30 — 
10 — 
40 — 

Class 2 
Max. Min. 

Per cent. 
— 91 
10 — 
50 — 
10 — 
90 — 

Class 3 
Max. Min. 

Per cent. 
— 83 
10 — 
50 — 
10 — 
170 — 

All the products must pass a No. 16 sieve (apertures 119 mm.) unless otherwise 

For use in bottle glass manufacture the limestone may contain up to 0-5 per cent. 
FezOa, with S1O2 and AI2O3 up to 15 per cent. Sulphur and phosphorus should not 
exceed 1 per cent. 

Bleaching Powder. For the manufacture of good quality bleaching powder, the 
starting point must be a high calcium limestone containing only traces of manganese 
and iron, both of which are said to be detrimental to the keeping quality of the 
powder. Clay should be absent, and magnesia is objectionable as it gives a deli- 
quescent chloride. The limestone, on burning, should give a fat lime which will 
slake readily to a very fine powder in twenty to thirty minutes and give a volume of 
slaked lime about three times that of the original lime. Open textured limestone or 
chalk often gives a better product than does a dense limestone. The lime should not 
contain more than about 0-5 per cent, of iron oxide or over 2 per cent, magnesia. 
The hydrated lime should not contain a large excess of water over the quantity 
necessary to hydrate the lime: the usual amount varies between 2 and 4 per cent. 

For the production of calcium hypochlorite solution, or bleach liquor, some 
manufacturers specify a fat lime containing about 95 per cent. CaO, under 5 per 
cent. MgO, under 2 per cent. AI2O3, and an iron content not exceeding 0-2 per cent. 
Sulphur, phosphorus and titanium compounds should not be present in appreciable 

Ceramic Uses. Calcium carbonate, which may be in the form of either ground 
limestone, marble, chalk or whiting, is used as a constituent of certain pottery glazes 
and enamels. The mineral should contain not less than 97 per cent, total carbonates, 
with not more than 0-3 per cent, of iron oxide, 2 per cent, of silica, and 01 per cent, 
of sulphur trioxide. A sub-division is made into two grades according to the relative 
amounts of calcium and magnesium carbonates; grade (I) contains not more than 1 
per cent, magnesium carbonate and grade (II) may contain up to 8 per cent. 
magnesium carbonate. 

Textile Industry. Lime is used in the boiling out, scouring and bleaching of 
vegetable fibres and for liming kiers. 

As regards chemical composition, the lime must contain a minimum of 94 per 
cent. CaO with the following maximum permitted percentages : MgO, 3 ; Fe203 + 
AI2O3, 2; Si02 and insoluble matter, 2-5; all calculated on a non-volatile basis. The 



maximum permissible percentages of carbon dioxide (CO2) are as follows : if sampled 
at the place of manufacture — hydrated lime, 3 ; quicklime, 5 ; if sampled elsewhere 
than at place of manufacture — hydrated lime, 5 ; quicklime, 7. 

It is recommended that the use of limes containing much iron in a readily soluble 
form should be avoided, as also should material containing a considerable amount 
of unhydrated magnesia. 

Leather Dressing. This industry consumes large quantities of both quicklime and 
hydrated lime made from high calcium limestone, particularly in de-hairing processes. 
If quicklime is used it should give a fine, smooth putty, the suspensions of which, as 
milk of lime, should be extremely slow in settling. High magnesian lime is sometimes 
used in preparing morocco leather, but for most other processes the presence of 
magnesia is regarded as objectionable owing to its slowness in slaking and possible 
damage to the skins by burning. A low content of iron or other metallic impurities is 
desirable as these may cause staining of the leather. 

Varnish Manufacture. Hydrated lime for this use should usually have a high 
content of CaO whilst MgO should be low and the material should not produce any 
darkening of the varnish. 

Calcium Carbide. Manufacturers of this product require a high-grade lime or 
limestone for incorporation with the carbonaceous matter. The consumption of 
limestone, or its equivalent in lime, is about 2 tons for each ton of carbide produced. 
Lime is frequently preferred as it entails less consumption of electric power. 

Some users claim that better results are obtained if the limestone is burned to 
lime before incorporation in the furnace mixture. The physical characteristics of the 
limestone are of considerable importance. In general, porous limestones on cal- 
cination yield a weak, powdery lime not capable of withstanding the abrasion which 
occurs in the carbide furnace. The most desirable material is a dense, massive type, 
such as mountain limestone, which will not crumble during processing. Some, but 
not all, coarsely crystalline limestones crumble on calcination and, hence, are not 
to be recommended for use in carbide manufacture. Oolitic limestone is often 
unsatisfactory owing to its associated impurities, and chalk lime, although suitable 
when sufficiently pure, often contains too much silica. 

Specification requirements of carbide manufacturers vary somewhat, but are 
usually within the following percentage limits: CaO, 95-97; Si02, 1-3; P, 001- 
05; other impurities, 2. Impurities regarded as objectionable include magnesia, 
alumina, silica, iron oxide, sulphur, phosphorus and alkalis. It is stated that the 
presence of silicon and magnesium in the carbide tend to cause too rapid evolution of 
the acetylene when the material is treated with water, resulting in production of a 
brown carbonaceous dust which clogs up the gas jets. Phosphorus is objectionable 
as it leads to the contamination of the acetylene with phosphene gas. The presence of 
magnesia in the lime is said to affect adversely the efficiency of the electrolytic 
process of manufacture; a limit of 0-5 per cent, of MgO is stipulated by some carbide 
manufacturers, although it is stated that lime containing as much as 1 -8 per cent, 
has been successfully used. The presence of much magnesia is said to reduce the 
fusibility of the melt and make the furnaces difficult to tap. Alkalis in lime, in the 
presence of silica, tend to form fusible products which interfere with the efficiency 



of the carbide. The requirements for lime to be used in the manufacture of cyanamide 
are similar to those for carbide. 

A.S.T.M. Standard Specification C 258-52 requires quicklime for use in calcium 
carbide manufacture to be substantially free from ash, core and dust and to be in 
pebble or lump form. The chemical composition is shown in Table 102. 

Table 102 

Quicklime for Use in Calcium Carbide Manufacture. A.S.T.M. C 258-52 

rr, , Per cent. 

Total lime, CaO, min 92 

Magnesia, MgO, max 1-75 

Silica, SiO a , max . . .20 

Iron oxide plus alumina, Fe a O s + A1 2 8 , max 10* 

Sulphur, S, max 0-2 

Phosphorus, P, max. 0-02 

Loss on ignition, on sample taken at place of manufacture . .4-0 

* Not over 0-5 per cent, may be iron oxide, FeaO a . 

Abrasives. Certain dolomitic limestones, on suitable calcination so as to avoid 
overburning, yield a lime which is utilized as a mild abrasive for polishing silver- 
plate, copper, brass, nickel and other metallic surfaces. One such material, known as 
Sheffield Lime, prepared by calcining a pure dolomite which occurs near Sheffield, 
has the following percentage composition: CaO, 57-30; MgO, 40-21; Si0 2 , 0-54; 
Alz03, 0-34; Fe203, 0-37; SO3, 017. A similar product is made in Bavaria and 
known as Vienna Lime. 

Carbon Dioxide. The chief industrial sources of this gas are the minerals lime- 
stone, dolomite, marble, magnesite or natural gas, the latter being used in the 
United States, Canada, France and Germany on a large scale and to a lesser extent 
in some other countries. Carbon dioxide evolved in certain industrial processes, 
such as fermentation and coke ovens, is also utilized. The gas has many uses such as 
for carbonating beverages, raising beer, in the manufacture of alkali by the Solvay 
process, in fire extinguishers, in sugar manufacture and as a refrigerant. In the latter 
connection it is also employed for sealing off (by freezing) quicksands and porous 
strata in shaft-sinking and oil-well drilling. 

When limestone or other mineral carbonates are used the material should be of 
high purity. As a general rule, the limestone is calcined in either mixed feed or gas- 
fired kilns in order to obtain as rich a gas as possible. In mixed feed kilns the fuel 
should be coke, as coal gives a gas contaminated with tarry matter which is difficult 
to remove. 

The gases from the kiln, which should contain not less than 30 per cent. CO2, are 
cooled by being passed first through waste-heat boilers and next through a solution 
of potassium carbonate. The solution is then run into closed boilers and heated 
under pressure, whereby the bicarbonate formed is decomposed with the liberation 
of pure CO2. This gas is removed from the boilers by suction pumps, dried by being 



passed over calcium chloride or other desiccant and run to the compressors for 
liquefaction. At 31° C. the pressure required for liquefaction is 1,036 lb. per sq. in., 
but at 0° C. only 520 lb. pressure is required. 

Water Treatment. For this purpose limestone is converted into either quicklime 
or hydrated lime. According to A.S.T.M. Tentative Specification C 53-52T hydrated 
lime for water softening should contain not less than 68-1 per cent, of available lime, 
equivalent to 90 per cent. Ca(OH)2. Quicklime for water treatment is covered by the 
same specification, which requires a lime free from core, ash and dirt, which will 
readily disintegrate in water into a finely divided suspension. The quicklime should 
contain not less than 90 per cent, of available lime. 

Silica Brick Manufacture. In the manufacture of silica bricks, silica in the form of 
massive quartzite or quartz conglomerate is ground until the particles are less than 
i in. size, lime, either quick or slaked, is added to the extent of 1 -5-3 per cent, with 
enough water to produce 5-7 per cent, moisture content. Shapes are moulded from 
the mixture, dried, and burned in shaft or down-draught kilns until most of the 
quartzite has been converted to tridymite or cristoballite. 

Quicklime or slaked lime for this purpose, according to A.S.T.M. Specification 
C 49-57, should contain not less than 90 per cent. CaO, and the following per- 
centage maxima: MgO, 4-5; Fe203 + AI2O3, 1 -5; Si02 and insoluble matter, 3; all 
calculated on a non-volatile basis. Carbonates, expressed as CO2, must not exceed 5 
per cent, on material sampled at the producing works, and 10 per cent, if sampled 
elsewhere. As regards physical properties, hydrated lime must show at least 99 per 
cent, passing a No. 30 (590 micron) sieve and 95 per cent, passing a No. 200 sieve 
(74 micron), when tested according to a specified method. Rapidity in slaking and 
fineness of the hydrated product are stated to be desirable qualities. 

Low grade lime is undesirable as it often slakes badly and may introduce fluxes 
into the mixture. Some makers claim that a magnesian lime can be employed if it is 
fully hydrated before use; others state that such limes slake slowly and irregularly 
and may produce bricks liable to crack spontaneously. 

Lime for Sand-Lime Products. The chemical requirements for quicklime and 
hydrated lime for use in the manufacture of sand-lime products specified under 
A.S.T.M. Specification C 415-58T are the same as under C 49-57 above. 

Grease Manufacture. According to A.S.T.M. Tentative Specification C 258-52, 
hydrated lime for this purpose should contain not less than 90 per cent, of available 
calcium hydroxide, Ca(OH)2, whilst magnesia, MgO, must not exceed 1 -5 per cent.; 
SiOa, 1 per cent., and iron oxide, Fea03, 0-5 per cent. The fineness, determined by 
wet screening, must be such that at least 98 per cent, of the material will pass a No. 
200 sieve and 95 per cent, will pass a No. 325 sieve. 

Mineral Treatment Processes. Considerable quantities of high calcium lime, 
either in the form of quicklime, hydrated lime or milk of lime, are used in flotation 
processes for the separation and concentration of minerals. In the cyanide process for 
the extraction of gold, lime is added to counteract the effect of soluble acid salts in 
the mine or mill water, as a coagulant to effect the settlement of slimes, and as a 
protection against soluble and insoluble cyanicides in the ore treated. 

For use in the flotation process the lime should contain over 90 per cent. CaO, 



magnesian or dolomitic limes being unsuitable. The lime should be of a type which 
settles slowly from a suspension in water. 

Other Chemical Uses. Various grades of lime are used extensively as neutralizing 
agents in many chemical processes, such as the manufacture of soap, arsenical 
insecticides, glue, gelatin, citric acid from fruit juices, and phenol. As a general rule, 
the lime should be fairly free from clayey material, silica, alumina and iron oxide, 
but magnesia is not generally objectionable unless the end product desired is a pure 
calcium salt. In the manufacture of table salt from brine, lime is sometimes added to 
precipitate magnesia as hydrate and to remove bicarbonates. Lime is used at some 
gas works for removing carbon dioxide and some sulphur compounds, and for this 
purpose should contain about 95 per cent, of CaO. 

For the manufacture of calcium arsenate or Bordeaux mixture, either quick or 
hydrated lime may be used. The quicklime should contain not less than 92-5 per 
cent, of available lime (CaO) and hydrated lime should carry not less than 90 per 
cent, of available calcium hydroxide (Ca(OH>2). The maximum permissible limit in 
each case for magnesia is 1 -5 per cent. 

Lime or limestone is largely used to neutralize the waste acid liquors from steel 
plate pickling works. Recent work in the United States has shown that for this 
purpose limestone gives the most satisfactory results, followed by hydrated lime, 
hard burnt lime and soft burnt lime so far as settling of the sludge is concerned. 
Dolomitic lime gives less sludge except when excess is used; then the excess lime 
causes precipitation of magnesium hydroxide. 

Sewage Treatment. Limestones or dolomites are sometimes used in the filter beds 
as hosts for purifying organisms. Stone for this purpose has to be screened to re- 
move fine dust and should be capable of withstanding conditions of weathering due 
to frost, etc. Impurities such as clay, pyrites, shale, chert and ochre are undesirable. 

The desirable physical characteristics for limestone for use in filter beds are (1) 
a minimum volume of pore spaces connected with the surface; (2) the pores should 
be small and evenly distributed; (3) the crystals making up the stone should be well 
interlocked and, if it is composed of granular material, the grains should be firmly 
bonded together; (4) the stone should be of uniform solubility; (5) it should be free 
from minerals which, under conditions of use, will oxidize or hydrate, pyrite and 
marcasite being particularly objectionable; (6) the surface of the blocks should be 
sufficiently rough to give anchorage for bacteria to grow; (7) as delivered, it should 
be fairly free from dust and fine rock particles which may clog the filter beds. A 
moderately high content of free silica is permissible if it occurs as evenly distributed 
fine crystals. 

The limestone is frequently submitted to a number of tests to determine its 
water absorption, rate of solution, behaviour when the water-saturated material is 
repeatedly submitted to freezing, hardness, toughness in use, and a quick weathering 

Agricultural Uses. Large quantities of ground limestone, quick and hydrated lime 
are used in agriculture principally to ameliorate soil conditions. The functions of 
lime in this connection include the improvement of the texture of clay soils by 
flocculating colloidal matter and so making heavy soil more granular, converting 



insoluble potash minerals to a form in which the potash is available for plant 
nutrition, providing a suitable environment in which soil bacteria can convert 
waste vegetable matter into humus and reducing the acidity of peaty soils. 

So far as can be ascertained there are no standard specifications for agricultural 
limestone; during World War II material containing as little as 10 per cent. CaO 
was used in some parts of Great Britain. Under the Fertilizer and Feeding Stuffs 
Act (1926), however, the percentage of CaO in burnt lime, hydrated lime or carbon- 
ate of lime must be declared by the seller and a differentiation made between " free " 
or " active " CaO and total CaO. 

Ground limestone is often used as a filler in compound fertilizers both to add to 
the weight and to prevent caking. 

Stabilization of Soils. Increasing use is being made, particularly in the United 
States, of hydrated lime for the stabilization of road surfaces. When lime is added 
in small quantities to plastic, fine grained clay soils, or to coarse grained (gravelly) 
soils containing a highly plastic binder, it decreases the plasticity of the soil and 
increases its compressive strength. As a stabilizer hydrated lime is most effective 
with coarse grained clay-gravels, granite gravels and related types. On the other hand, 
quicklime, although more difficult to handle, gives similar results at less cost. Men- 
tion may be made of one example of soil stabilization as an indication of quantities 
used: A mixture of 80 per cent, soil, 15 per cent, fly ash and 5 per cent, of high 
calcium hydrated lime laid 4 in. thick proved satisfactory as a road stabilizer. In 
1958 about 240,000 tons of lime was used in the United States for road stabilization. 

Road Paving Mixtures. Considerable quantities of limestone or dolomite are 
used in roadway construction, particularly in what is termed street asphalt. The 
source of the raw material may be either a naturally occurring bituminous limestone, 
such as those worked in Switzerland, France and the United States, or a mixture of 
asphalt, bitumen or tar with sand and ground limestone; this latter compound is 
sometimes known as " British Asphalt." Street asphalt is the name applied to the top 
wearing coat or surface of roadways, and is usually H in. to 2 in. thick. Its composi- 
tion varies but may consist of 15 per cent, asphalt, 75 per cent, graded sand, and 10 
per cent, limestone dust. Limestone for this purpose is sometimes specified to contain 
from 60 to 80 per cent, of material passing a 200-mesh sieve; other specifications 
require all the material to pass a 30-mesh sieve, with not more than 15 per cent, 
retained on 100-mesh and not over 20 per cent, on 200-mesh. 

For use in asphalt concrete, the limestone may be used in sizes from 3 in. down- 
wards according to the nature of the work. 

Limestone is also used in mastic flooring and for this purpose screenings are 
used from J in. down to dust. For the finer qualities of mastic flooring it is sometimes 
specified that 80 per cent, of the limestone shall pass a 200-mesh sieve and that 50 
per cent, of the particles shall be less than 001 in. in diameter. The fragments 
should preferably be angular rather than rounded. 

Rock or Mineral Wool. Considerable quantities of impure limestone are used, 
particularly in the United States, in the manufacture of rock wool which is a useful 
"heat insulating material. It is produced by melting the mineral, often in a cupola 
furnace, and then letting it fall in a stream of drops in front of a jet of steam or air 



under pressure. The product so obtained consists of a mass of glassy fibres mixed 
with unfibrillated globules; it is next treated to remove the globules and coarse 
brittle fibres. The raw material used may be a naturally occurring mineral product 
or a mixture of dolomitic limestone and an argillaceous material. Apparently there 
is a wide variation in the chemical composition of the mixtures used, but one 
authority gives the following as representing the average percentage composition of 
nine different makes of rock wool produced in the United States : CaO, 31-3; MgO, 
13 8; SiO a , 38-8; AI2O3, 11-5; Fe as Fe 2 3 , 21; alkalis, 31. Another authority 
states that the limestone or dolomite used should contain from 45 to 65 per cent, of 
carbonates of lime and magnesium. 

The manufacture of mineral wool in Great Britain has been in operation since 
1947 in the Matlock district of Derbyshire, using a mixture of limestone containing 
26 per cent. MgO, a clay carrying about 35 per cent. AI2O3 and fluorspar; the plant 
having a capacity of about 50 tons per week. The mixture is charged, with alternate 
layers of coke, into a cupola furnace, air being blown in through inlets in the hearth. 
The melt is drawn off in a thin stream, which is subjected to a blast of 
superheated steam to give a mixture of wool-like fibres with some solid globules 
(" shot "). The product, marketed under the name of " Cawdonite," weighs about 
7 lb. per cu. ft. and can be heated to 800° C. without losing its wool-like character. 
It is a good electrical insulator, melts between 1,400° and 1,450° C, and has a ther- 
mal conductivity at room temperatures of 0-25 B.Th.U./in/ft. 2 /hr./.°F. difference in 
temperature. The fibres range between 1 and 1| in. in length and have an average 
diameter of 0002 in. 

A mineral wool named " Rocksil " is made by the Cape Asbestos Co. Ltd. at 
Stirling, Scotland, from a mixture of dolomite from the Argyll Hills and fireclay 
from Stirlingshire. The ground mixture is heated to about 2,800° F., the molten mass 
extruded into fine threads which, on cooling, form a white resilient fleecy mass of 
long fibres of about 1 microns diameter. The fibres are mechanically self-supporting 
and do not " settle " under vibration. It has a specific heat of 0-21 B.Th.U./lb.fF. 
and a " K " value of 0-25 B.Th.U./in./ft. 2 /hr. at atmospheric temperature. It is non- 
hygroscopic, fungus and rot proof and as supplied has a density of about 4 lb. per 
cu. ft. It is extensively used for the sound insulation of buildings and heat insulation of 
pipelines. It can withstand temperatures up to 1 ,400° F. without sintering or breaking. 

Mine Dusting. Various types of finely ground mineral products, including lime- 
stone, are spread in dry bituminous coal mines in order to lessen the spreading of 
fine particles of coal in the air and so to reduce the risk of explosions. Limestone is 
frequently employed for this purpose; it should be light coloured, and free from 
carbonaceous matter or any appreciable percentage of free silica. The Coal Mines 
General Regulations M. & Q. Form N 128 requires that, of the materials passing a 
60-mesh B.S.I, sieve, not less than 50 or more than 75 per cent, shall pass a 240-mesh 
sieve. It is now possible to produce a waterproof ground limestone for use in damp 
mines. This material is often placed on hanging trays which, when rocked by the 
force of explosion, drop the limestone in the form of a curtain which prevents the 
spread of the explosive flame. It is sometimes specified that 90 per cent, of the 
waterproof ground limestone must pass a 60-mesh sieve. 



The United States Bureau of Mines specifies that ground limestone for use in 
mine dusting shall be all ground to pass a 20-mesh sieve, with 50 per cent, passing a 

Optical Uses. A variety of calcium carbonate known as Iceland spar finds a 
limited use in optical instruments such as polarizing microscopes. The mineral is 
doubly refracting and, when suitably cut, has the property of converting an 
ordinary light ray into plane polarized light. A familiar example of such use is in the 
Nicol prism. The principal characteristics which make Iceland spar of special value 
for such purposes are its high degree of purity, perfect crystalline structure and 
transparency. The mineral must be in pieces at least one inch long by half an inch 
thick, colourless, perfectly transparent, and free from cloudy inclusions, cavities or 
foreign substances. It must also be free from internal irridescence, due to incipient 
cracks along cleavage planes, and from twinning. 

At one time the only regular source of supply was the quarries near Eskifjordur 
in Iceland, but more recently good quality material has been exported from the 
Kenhardt district of Cape Province, Union of South Africa, and a small output has 
also been obtained from some of the Western States of the U.S.A. and Spain. 


This name is applied to calcium carbonate of good white colour in a fine state of 
division. Various grades are known commercially as Paris white, Gilders whiting, 
English cliffstone, etc. Whiting may consist of naturally-occurring calcium carbonate 
suitably pulverized, or it may be obtained by chemical precipitation. In Great 
Britain the term " whiting " is usually applied to a product obtained by pulverizing 
and levigating chalk or chalk marl. 

In some localities, where convenient deposits of suitable chalk marl are not 
available, a substitute for whiting is prepared by finely grinding a good white 
marble to pass a 325-mesh sieve. Such material often differs from chalk whiting by 
having sub-angular instead of rounded particles and a rather lower oil absorption. 
In Canada this material finds use in the manufacture of linoleum and oilcloth, 
explosives, putty, and as a filler in newsprint. A white dolomite is similarly treated 
and used in Eastern Canada. 

The desirable characteristics of a high-grade whiting are a good white colour, 
fine particle size and freedom from grit. 

The value of chalks and whitings is affected by many considerations, such as 
fineness, time of settling and workability, most of which have little reference to its 
chemical composition. 

In this country, sources of supply can be roughly divided into the soft deposits 
of chalk found in south-east England, particularly in the Thames valley, which 
furnish various grades of whiting by fairly simple crushing and levigation